If there's no incentive, there's no race.
I, personally, also like the up-votes costing karma. It'd make the act much much more costly to perform, so high voted comments will be more likely to be selected on content than laughs.
Regarding the "laughs" I don't really understand what the big deal is. I like a funny/sarcastic (read: not stupid) comment that shows at least some insight or understanding of the matter or just pokes fun at a particular view. This is necessary and healthy for a discussion.