I would prefer a system akin to old forums. Posts are worth X experience points(or whatever you want to call it) based on word count(and possibly some other factors). Maybe aside from ranking the page/comments, votes could also be used to determine how good at "promoting discussion" the post was. Upvote if the post promotes discussion(even if you disagree with it), and downvote if it's just trolling gibberish nonsense. Then use the upvote/downvote ratio to determine how much of the experience points are gained or lost from the person's reputation.
So for example, say a certain post was worth 100 exp based on its specific word count. And it has a 78% "this was good discussion" upvote ratio. The user would gain 78 exp. Longer, but well thought out and not spammy posts would in theory rise to the top while still rewarding shorter posts as well and discouraging quick spammy stuff.
This would of course require votes to return to "this does/doesn't promote quality discussion" vs "I like/agree with this".