Day 1.The diesel train speeds out of Edinburgh Waverley station and south along the newly-reopened Borders Railway line. It climbs up to almost 1,000 ft at Falahill then drops down through the lovely Gala River valley towards the final destinations of Galashiels and Tweedbank. As befits a half-hourly service, the train is busy but not crowded.

Equipped with a wealth of information about the destinations on this 31-mile trip, both from the dedicated route website and an excellent guide pack produced by local company Locus Focus, you appreciate their history, culture and tourism offerings.

And you understand a little more about the success story that Scotland’s newest rail line is becoming. Opened last September after major investment of £300 million, its passenger numbers are soaring: in its first six months the line carried almost 700,000 people – 22 per cent more than expected – with many being daily commuters to Edinburgh.

The route’s promoters, including the likes of Scottish Enterprise, claim an annual economic gain to the Borders of £30m. Impressed, you wonder if Scotland’s under-invested railway has actually got its act together at last.

Then comes Day 2. Boarding an elderly two-coach diesel train at Oban station, you encounter full seats and little luggage space. It’s one of only six services a day to Glasgow, so no surprise it’s busy at the height of the tourist season. Still, you’re looking forwards to the spectacular journey down the famous West Highland Line through some of our most beautiful scenery.

Alas, rampant lineside vegetation means much of that scenery is shrouded from view, branches whipping against the dirty windows as the noisy carriages rattle along at a sedate speed. Frustrated, you find your thoughts turning to such burning issues as....why does it take over three hours in this day and age to cover 101 miles by train? Why is this renowned line operated by uncomfortable, inadequate rolling stock? Why are there so few services in summer? Above all, why does a route trumpeted as Britain’s best scenic railway only attract 170,000 passengers a year to a destination whose port is home to ferries that service some of Scotland’s most economically fragile Western islands?

The contrast between the Borders Railway and the West Highland Line is stark. Both are marketed by ScotRail, VisitScotland and a number of private rail booking firms under the Scotland’s Great Scenic Railway Journeys label. So they’re likely to attract more tourist traffic than our other mainline rail routes. Both explore some of our most scenic landscapes. Both play important roles in the local economies of the communities they serve.

But the reopened Borders route, with its high frequency of service reinforced by modern marketing methods, is visibly delivering economic activity. The under-served and under-marketed Oban line is a brake on the economic potential of the Lorn area of Argyll.

What is it with our public transport system and government’s inability to view railways as powerful agents of economic growth and sustainability, and invest accordingly? For a fraction of the cost of reopening the Borders Railway, the West Highland Line including its northern branch to Mallaig, not to mention the equally under-served Kyle line from Inverness, could channel thousands more passengers and their cash into some of our most needy communities.

We are promised "improvements" to these routes under the Scottish Government’s deal with ScotRail operators Abellio. But what is surely needed is a wholesale re-evaluation of the importance and potential of our scenic rail heritage.

So let’s escape government’s narrow mindset to dream a little, about what should be possible with an imaginative business plan, a dash of modern technology and some decent rolling stock. This is what a tourist could experience in 2020.

After an excellent seafood meal at one of Oban’s pier restaurants, you board the Glasgow train and settle into your comfortable reclining seat in the Observation Coach. Weaving south past Connel Ferry, Taynuilt and Tyndrum, along Lochs Awe and Etive, you view the magnificent scenery through the panoramic windows and learn about the passing landscape and its history through the seatback touch-screen information system at your fingertips. Armed with a chilled glass of wine from the refreshment trolley, you listen to the contented chatter of other tourists around you.

The visible success of the new Borders Railway demonstrates yet again the consistent adage that investing in modern train services produces viable economic benefit. Do we really have to tolerate second-class services on Scotland’s world-class scenic rail routes?

Alastair Balfour is a former business journalist, publisher and strategic adviser.