What should the content of that vision be? Clearly, it should be demarcated from the overweening anti-cosmopolitanism and religious fundamentalism of the GOP base. But critique is the least of it.
The real question is, what is the Democrats' positive vision of the country? Personally, I think there already is one, and it's actually pretty simple: Democrats believe in a vision of America as a tolerant and open society based on the scientific, Enlightenment ideals of the founding fathers. This vision shouldn't be couched as a head-on attack on religion, but rather as a pro-science, pro-empiricism agenda. For example, Kerry's best moment in the whole campaign was when he said to Bush in the first debate, "You can be sure, and you can be wrong." That was exactly the right way to make the empiricism-versus-faith point.
Which raises a crucial point: the Democrats must dramatize their vision in down-to-earth terms, symbolic terms. Ever since Reagan, the Republicans have been much better than the Democrats at finding emblematic, expressive mechanisms for explaining themselves. (Which is odd: since all of the ad people and movie people are Democrats, why are the Republicans so much better at spin?) The Democrats have a sad tendency to be very literal minded -- i.e. Kerry saying, literally, "that's not my gut."