The bigger problem for Democrats nowadays is that no matter how careful they are not to display a Stevensonian condescension, they'll end up being accused of it anyway. Gore and Kerry were accused of "elitism" not because they acted like elitists, but because accusing Democrats of elitism is a standard tactic employed by Republican campaigns. The Democrats could nominate Archie Bunker or some Capra-esque Everyman and their nominee would still be accused of elitism. Whether or not the Democratic candidate treats voters as though they were unenlightened idiots in need of re-education, they will be accused of doing so. And, as Perlstein points out, if that accusation sticks they will lose.
Related to this is what we could call the Smartest Guy in the Room dilemma. Nobody likes the Smartest Guy in the Room. Nobody likes to be lectured. Gore, God bless him, has always had a problem with this. He strikes a lot of people as a very smart college professor giving a lecture and that rubs them the wrong way. Even when they have to acknowledge that he really is a very smart guy. Even when they have to acknowledge that his lectures are, inconveniently, true and urgent and even necessary. They end up resenting him for being right rather than admiring him for it.
"Favorite Teachers" -- Fred Clark over at slacktivist.com