When I upvote a question I do so because I think it's a good question. Other people would benefit from seeing the question or maybe be able to add important answers. To increase exposure of upvoted questions, I suppose that upvotes should bump a question to the top of the front page.
This would give upvotes on question more meaning than just incentive to ask good questions. It would give upvoted questions additional exposure and increase the chances for good answers on questions people care about. It would also be useful to call some attention to old, unanswered questions people are still interested in.
Downvotes instead shouldn't have any special effect.