The smartest post-election analyses I've seen from conservatives emphasize the idea that the Republican Party needs a message that's broadly appealing to the interests of middle class families. And I think that's all right. But if you look at Andrew Gelman's chart of income and voting behavior you'll that when Republican presidential candidates do better they tend to do better across the board.
It's always the case that the poor vote for Democrats and the rich vote for Republicans (but by a smaller margin) while the middle class is contested terrain. But compare the GOP's best year (2004) to its worst (2008) and you'll see a dramatic shift among low-income voters to the Democrats. Whether you want to attribute that to fundamentals or message or whatever, the same point holds—the shifts are pretty broad-based and whatever it is that makes a party more popular with the middle class probably also makes it more popular with the rich and the poor.