At some point, shouldn't content like the latter be identified as either applause lights or guessing the teacher's password? And, theoretically, be documented better in the wiki than the original posts?

Maybe, but the idea is to make the best content the most visible. If applause gains higher visibility than content, the system has failed even if the users are able to identify which is which after having seen them both.

I haven't spent any time on the wiki, though, which suggests that either I am doing it wrong or that the wiki is not as high-quality as the posts yet.

I think people use the forums more instead of the wiki because the forums are more social and interactive. (I see this is a real benefit of forums over wikis, not as a bug that people have)