I've had some time to think about it and I think I actually like the current setup. "Boost" provides more visibility to a post, while "upvote" and "downvote" is synonymous with agree/disagree.
In a way, I can disagree with someone AND boost it. Disagreeing with someone doesn't have to be hostile. I think it would be healthy if a community could disagree with each other in a civil manner.
I also like that if someone disagrees, that person cannot influence if the post gets less visibility.
VoxAdActa