I'd wager virtually nobody would vote. The only exception being if the benefits of receiving a vote outweighed the costs of casting it, in which case small groups would agree to upvote eachother's posts. You'd also have more problems with multiple account sign-ups just to upvote nodes.

If you want to make vote's more valuable, simply decrease the supply, then most people would use them more carefully.

Or you could just get rid of the whole silly system. Or make XP private. Or forget about the whole thing ;-)