Ok, probably nobody will read this, since I have few friends, foes, freaks and fans, but I had a thought worth posting.
I comment only a couple times a week, occasionally posting something I know will swallow a little Karma, but usually trying to be significant or occasionally funny.
The egoboo of being modded up is nice... but I'm always happier when someone replies. It's a conversation, perhaps a debate. More often than not, I'll reply to that poster.
The further down in the tree, the less likely it is to be modded -- because people don't look down the trees, and because the reply to the reply is likely to be a day later.
That makes me think that rewards on this site should be weighted towards replies, esp. replies that get modded up. And a mod on a reply is probably worth more than a top-level mod.