High quality, contentious comments should be front and center in the discussion. People also seem to like expressing their opinion by clicking, which acts counter to this goal.

I find myself wishing there were two values: agree/disagree and valuable/useless. Not because I think we particularly care about the agree/disagree ratio (we can form our own opinions, and comments are always more interesting valuable in this regard anyways), but because then it would absorb opinion votes, removing them from the valuable/useless score that helps determine where a comment is located and how it is colored.