I think something that would incentivize those longer-form interactions would be to remove the upvote/downvote system and replace it with something similar to what SA had back in the day, where you could label posts with "Insightful", "Funny", "Off-topic" and the like. I find that too many people will only say things that they know will get them karma, which leads to that hivemind that everyone hates. Having a system where you can put a numerical value on someone's "importance" to the site will only lead to users minmaxxing their responses.