SOME time last year I found myself on board the Renfrew Ferry (as I'm afraid I still call it) to see a man in a dodgy wig and suspiciously polyester-looking suit pretending to be David Bowie.

I'd seen the real Bowie at the SECC in Glasgow back in 1995 but I couldn't envisage ever seeing the man in the flesh again, given that it seemed he'd pretty much given up on making and performing music, so a night out to see a tribute band play songs that had been part of my life since I was a kid felt like a harmless guilty pleasure.

The band – Absolute Bowie – were, wig apart, actually really good. A kind of entertaining, inevitably faded, fifth-hand facsimile of the real thing. The whole night felt like an enjoyable but rather sad acknowledgement that the greatest, most thrilling, most important pop star of the last 50 years was now the simple, bittersweet stuff of nostalgia.

After all, Bowie hadn't been seen on stage since chest pains during a gig in Germany in 2004 had led to emergency angioplasty for a blocked artery. And apart from the odd acting appearance – in the Christopher Nolan film The Prestige and playing someone like himself in Ricky Gervais's sitcom Extras – that had been more or less the last we saw or heard of him. So much so that it was generally thought – though never actually said – that he had retired from the music industry. There were even dark rumours that he was seriously, perhaps terminally, ill.

So the giddy reaction to the release last Tuesday (his 66th birthday) of a new single, along with news of an album to come in March, was understandable. Because it was so surprising. Indeed, when I first heard radio presenter Nicky Campbell say the words "Bowie single" I thought: "How sad. He's separated from Iman."

Since Tuesday, Bowie fans have been popping up all over the media and Twitter to say how excited they are at the news. Some of them – Steve Strange, Boy George – have been the usual suspects. Others (on Wednesday I heard the BBC's business editor Robert Peston raving about Bowie's "cool androgeny") were perhaps not. What all seemed to agree on was that the new single was rather good (which it is: a fragile, lovely, very human thing that sees him revisit his Berlin days) and its unexpectedness: the absence of three months of trailers telling us it was happening, as tends to be the norm these days, was wonderful. Everyone was thrilled that Bowie could still surprise us.

There was a time when surprise was in pop's DNA; when rampant neophilia was part and parcel of what we expected from our pop stars. And Bowie was better at it than anyone else. For a decade at least – from the early 1970s to the early 1980s – he was pop's avant-garde, mining fashion and modern art and literature and reconstituting it all within his own alien outsider persona. After various false starts at the end of the 1960s, he launched his Ziggy Stardust persona by announcing to the press that he was gay (even though he was married and a father to Zowie – now film director Duncan Jones) and draping his arm around guitarist Mick Ronson on Top Of The Pops while singing Starman. That was enough to startle some. Simulating fellatio on Ronson's guitar during his gigs probably sealed the deal.

Bowie was a space-age dandy come from Mars to

turn us on to sex and Droogy violence (A Clockwork Orange was one of the many influences drawn on by Bowie, ever the cultural magpie). He was immediately the hero to every gay kid, as well as every straight kid who didn't buy in to the prevailing macho, misogynist culture of Britain back then – a culture whose parameters were marked out by Enoch Powell and the Carry On movies.

It helped that the music was thrilling, of course, with his band The Spiders From Mars recasting basic rock and roll with a Weimar decadence and a flying-saucer sheen. Bowie was glam in every sense of the word.

That was something to be suspicious of, though, for some critics. They tended to be the kind who preferred perspiration to inspiration. Some complained that he was all surface, that his constant image changes were the mark of shallowness. I remember the author Nick Hornby attacking Bowie for his chameleon qualities, not understanding it was that which made him fascinating. Such reactions suggested a fundamental misunderstanding of pop, which has always been about sound and vision. Bowie was both pop star and pop art.

A few years after the Ziggy era, and following a trip to America to invent plastic soul, he decamped to Berlin to reinvent himself again in the company of Iggy Pop and Brian Eno, and made his Berlin trilogy which mixed up Cold War atmospherics and huge, swelling electronic soundscapes – arguably pop's finest hour that decade – before dressing up as Pierrot and inviting the nascent New Romantics to join him in the video for his single Ashes To Ashes.

Everyone who was anyone in British pop in the 1980s was influenced by, or probably wanted to be, Bowie. Even into the 1990s he was teaming up with Goldie and Trent Reznor and exploring drum and bass on his 1997 album Earthling. He never stopped wanting to do new things (even if the rest of us weren't really wanting that from him any more).

His 10-year retreat has given his legend time to settle, for us to overlook his missteps – the Tin Machine era, that duet with Mick Jagger, saying the Lord's Prayer during the Freddie Mercury tribute concert at Wembley and being photographed making what some thought was a Nazi salute at Victoria station (proof that taking copious drugs was never, as was widely advertised, the gateway to knowledge – Bowie later insisted he had "just waved").

Enough, too, for us to overlook the fact that his new album is coming out in March, the same time as a major exhibition devoted to his past at the V&A in London; an example of typical music-industry synergy if ever there was one.

His reappearance has inevitably led some to suggest it is a rather sad reminder of what pop music has lost in recent years – that his very presence is an indictment of the conservatism of current pop, it's Guetta-isation, you might say (if you are up on your ubiquitous DJs-slash-remixers). Who apart from Lady Gaga pushes the envelope the way Bowie did? (And for all her magpie tendencies and alien glamour, even Lady Gaga's music is often pretty standard R&B, it should be said).

"Bowie seems the ideal icon for these uncertain times," the Telegraph's music critic Neil McCormick suggested the day after the single's release, "the kind of pop visionary who could bring the blurred possibilities of a disintegrating music culture into sharp focus."

That's a lot to ask of a 66-year-old man, no matter what the glories of his back catalogue might be. I also suspect it misunderstands why Bowie mattered back then and why he couldn't possibly matter in quite the same way if he appeared now.

Almost from its inception, pop music was oppositional. It was concerned with difference, with youthfulness, with everything grown-up society frowned upon ("Be childish. Be irresponsible. Be disrespectful. Be everything this society hates," as Malcolm McLaren said to wannabe punks). Often that opposition was merely surface deep – a pose for effect – but now and again it was in pop's very bones. Either way, it didn't matter. To the mainstream culture – to the government and newspapers and the police; to the grown-ups – pop was the enemy whether it meant to be or not. How could it be otherwise? It was even name-checked as part of the unholy trinity of youthful evils: sex and drugs and rock'n'roll.

That idea of pop as something to be inherently mistrusted lasted a long time. Remember, it's fewer than 20 years since John Major's government passed the Criminal Justice and Public Order Act in 1994, with its infamous ban on music "wholly or predominantly characterised by the emission of a succession of repetitive beats" in an attempt to curtail rave culture. Pop culture was often the principal area in which that now hoary old phrase "the generation gap" manifested itself. In the 1960s that gap was political (over the Vietnam War, most visibly); in the 1970s and 1980s it was often sexual (Bowie was one of the outriders of gay liberation even if, in the end, he downplayed his sexual fluidity).

But those huge fissures between them and us, between young and old, have largely closed now. We have a Prime Minister who claims he loves The Smiths (the ultimate example of 1980s outsiders) and The Jam's Eton Rifles, for goodness sake. We have Public Enemy songs soundscaping the Paralympics and we have had Iggy Pop (Bowie's friend, and, like him, a one-time notorious drug addict) selling car insurance. The fact is, we are all pop's children now. There may be a few middle-class parents who are still listening solely to Bach and Beethoven, but they're the minority. (Were they ever anything else?).

More than that, though, the culture wars which pop helped fight have been won. Yes, racism and sexism and homophobia still exist. But the consensus is – some ridiculous medieval religious spokesmen aside – that these are all bad things. There are exceptions (we seem to have forgiven Chris Brown very easily for his attack on then girlfriend, Rihanna). But even so, Britain is now a country proud of its mixed-race athletes and gay and lesbian pop stars. In that context, pop can't mean as much as it used to. It's no longer quite the badge of honour it might once have been.

It has also been watered down by the domination of light entertainment. Simon Cowell's dead hand on the music business through The X Factor has played a part in the homegenisation of pop in recent years. And so Gary Barlow – the Richard Carpenter of the 1990s and noughties – is everywhere: on the telly, the radio, on a stage near you.

That's not to say that there aren't great records being made, of course. (I'll let you name your own.) But the idea of pop as the central narrative to our lives – which it was for some of us for so long – seems more difficult to sustain. (I am sure there are some teenagers and twentysomethings scoffing as they read this, but I think it's true.)

Some time back in the 1970s, Michael Parkinson interviewed the film director Orson Welles. Why, Parky asked the great maverick, did Hollywood no longer create stars as luminous as it did back in the 1940s? Welles said it was simply because movies didn't matter as much. Pop stars were the new movie stars.

WE'VE moved on again since then. These days, we are obsessed with reality TV stars and Premier League footballers, I guess. Look hard enough and I'm sure you can find some vague notions of "alternative", whether it be in nu-folk or electronica. But these are locked into their own territories. We are all niche consumers now. The idea of pop as a transformational force that energised everything from Woodstock to Band Aid has surely gone.

What does that leave us with? It leaves us with a 66-year-old man nostalgically revisiting his past and reminding us that as well as once being a great – no, the greatest – pop star, he was also a pretty good musician. Written down, that seems diminishing. It's not meant to be. For a long time David Bowie was for some of us the most important person on the planet. It's cheering to think he is still out there, alive and well and making an effort.

And that's not just about us feeling nostalgic. That's about us feeling love. Love for someone who helped change our vision of the world. We were lucky enough to grow up in a time when pop – much more than politics – mattered enough to be able to do that.