I hear where you're coming from. I think eNotes does a better than decent job of organizing a rather vast quantity of material on the site, making things searchable and orderly. Thinking about how to make it even better can't hurt though.
There is a "great discussions" sections of eNotes that seems to be a selection of discussions picked by the eNotes staff. This would seem to address the question of how to present an archive of high quality discussions, at least to some extent.
Most of the discussions that make the "great discussions" section receive many posts before going to that section then receive many more upon being moved there. The quantity of responses seems like it can be a good indication of a thread's quality. Maybe weighting discussions according to the number of discussions as well as the five-star rating system could suffice to separate the wheat from the chaff, as you say.
Maybe this is already being done though. Each category/subject/topic already has a "popular discussion" tab in its discussion section.