(This is something that I wrote on kottke.org.)
I don’t know if this is a good idea, but it’s an idea: Include any “top comments” after the post text in the RSS feed items. As a way of drawing people in to the discussion. And maybe, on the website, a way to filter comments to only see the “top comments”?
Not to say that the rest of the comments aren’t worth reading, more that there will be people who wouldn’t bother to read comments and a way of highlighting the good ones, and demonstrating that it’s worth reading comments, and contributing, might help?
See on kottke.org.