Most of what you do is for expressive value anyway, so you shouldn't feel guilty about voting, if indeed you vote. The people who think they are being instrumentally rational by not voting are probably deceiving themselves more. They are actually engaged in an even less transparent form of expressive behavior (protest against the voting system) and yet cloaking that behavior under the guise of instrumental rationality. The best arguments against voting are simply if you either don't like voting or if you don't know which candidate is better. High-status people hardly ever offer the latter justification, even though the split of opinions among high-status people suggests that not all high-status people can in fact know which candidate is better.
In other words, both voting and not voting are motivated by the thought that you are better than other people. I am glad that we have an entire day devoted to this very important concept.
I would amplify Tyler's remarks and say that if you are at all inclined to not vote because it is instrumentally irrational, then you are probably a very well-informed and intelligent voter, and ought to feel especially good about voting, if you do. I'm not voting today, but that's simply because I didn't change my registration when I moved. I like voting. I usually do vote on big elections, and I vote expressively. I'm a bit disappointed to not do it this time around, since I would like to almost vote for Barack Obama before finding myself paralyzed by the Holy Spirit and then finally voting for Bob Barr. I would also like to vote for absolutely every Republican running for absolutely every other office. I learned a new phrase this weekend in NYC from an ex-roomie : “cognitive Madisonian.” I'm one of those.