Nick Confessore points out that the Democrats need to be smarter about exploiting the state ballot measure system to help increase turnout. That's obviously a good idea, and I think I have another one. Republicans have always been good at coming up with really bad ideas which are very popular with voters (say, term limits), and making it a central campaign issue. Most of these things never actually become law, because they're actually really horrible, but they're useful for scoring points.
I think the Democrats need to come up with a few of these. Get creative...