I realized just realized that our maps of states won by Republicans and Democrats by income group (see here, for example, also recently posted by Matthew Yglesias) are from 2000, not from 2004. We also mislabeled these in Plate 3 of the Red State, Blue State book. My bad. Here are the maps and scatterplots based on exit polls in 2004:
Not so different from 2000 (especially when you look at the scatterplots), with the most notable difference being Kerry’s strength in New England.
Fascinating breakdown. Would it be possible to make your raw data available on Many Eyes for use in a collaborative visualization that I'm working on?