Your comment brings to mind something I want to do with @spaminator. Find a way to run a contest to encourage users to have a conversation. I just haven't figured out how yet. Or maybe I have...

@patrice, you might consider touching bases with @merej99 who organized and ran the very successful "Community Engagement Challenge" a couple of months back-- 10 days of monster levels of engagement, creativity, posting, commenting, voting. I think we actually had one post that reached 700+ comments "in dialogue." Part of what made it cool was that we also had a fair number of dolphins involved... so newcomers got to experience "fair rewards" for well crafted comments.