He said the Scottish response to the Better Together campaign's warnings about the economy and declining oil revenues risked receiving a response of "who are they to come up here and tell us what to do?"
"We'll make our own minds up, thank you very much," will be the likely response, according to the Highland MP.
Calling for a clearer pro-Union prospectus, he explained: "If you take, for example, the recent figures on the state of the Scottish economy, the decline in the oil revenues and so on and so forth, I'm not sure that the right response to that from our point of view is to say: 'There we are, we told you so, Scotland could never go it alone'.
"I'm not sure that's a resonance that you can establish with the people and I'm not sure it's the right one anyway."
Better Together launched in 2012 with the message that Scotland could be a successful independent country but that it is stronger in the UK.
Since then, unionist parties have said Scotland could not formally use the pound and that its rising deficit following a recent dip in oil revenues points to a volatile economy.
All parties have offered stronger devolution if Scotland votes No but have not said what powers Scotland would receive.
Mr Kennedy said: "It would be better if we had a more coherent blueprint to put to people to say 'voting No means Yes to this distinct proposition' as opposed to, well, something that will be worked out in due course. Because then, you're open to exactly the accusation that we're making of the other side."
Meanwhile, Labour's Jim Murphy said Scotland faces a choice between two versions of a changed future - one of more devolution within the UK or one of uncertainty and disruption outside it.
On the eve of the publication of Scottish Labour's policy commission on more powers for Holyrood, the Shadow International Development Secretary said in his first major referendum speech: "Back in 1997, Labour won the General Election on the crest of the sentiment that things can only get better. Fast forward all these years and there's a group of Scots who worry that things can't get any worse.
"I know that winning this referendum isn't just about proving how things can indeed get worse with independence. This isn't a choice between the current status quo versus the uncosted uncertainty of us turning the rest of the UK into a foreign country. Scotland faces a choice between different versions of change."
Mr Murphy told his audience in Glasgow that devolution of tax, wages and welfare powers could feature in Labour's offering today, noting: "We need an increased minimum wage and more people on a living wage.
"Over the next six months and one day it will be increasingly clear that the referendum choice is between the disruptive risk of change with the Nationalists versus further devolved change as part of the UK."
However, the SNP hit back. Angela Constance, the Scottish Youth Employment Minister, branded Mr Murphy's speech "deeply hypocritical" given he had "failed to show up when the SNP tried to stop the Tories abolishing the 50p tax rate, whose party abolished the 10p tax rate and who is part of a campaign almost entirely funded by Tory business figures".
Elsewhere, vice-admiral John McAnally called independence as "the biggest strategic threat faced by our armed forces" and said the UK would be forced to give up its nuclear deterrent, would lose its seat on the UN Security Council and Scotland and England would be reduced to "two struggling nations on Europe's periphery".