You're right, the MOR discussion threads aren't very well organized for that. They work well enough for having an ongoing discussion, but not so well as an archive of the discussion that's already happened.

If you have a particular subject in mind and you want to see what's been posted about it, the simplest thing is probably to search the thread(s) for relevant keywords, including the chapter number. You could either use ctrl+f on each one of the threads that might contain relevant discussion, or the site's search function.

Don't worry so much about duplicating previous comments. It's worth doing a quick search to try to avoid it, but when it happens it's not so bad (especially with threads like these ones).

If you don't have a particular subject in mind and you just want to skim the discussion to see what's interesting, I don't have anything better to suggest than sorting by karma points.