People often run into problems where their "good enough to post" threshold creeps up and up. (...) Sometimes people handle this by dividing their writing into a formal blog and something casual.

Seems to me the best solution would be to have two blogs, post everything on the first one, and later repost/rewrite the most successful posts to the second one.

Probably depends on whether you want to have a discussion below your articles, because this strategy could mess with the discussion flow. However, I am personally quite scared of the idea of having to moderate comments on my blog; if my blog would accidentally happen to be super popular, the moderation could become a nightmare. I would probably go with the "only approved comments are displayed" approach, which slows down the discussion a lot.

With the suggested approach (repost top posts on the other blog), people who regularly read the first blog would probably not visit the second one. But it would be a good starting point for new readers, and a good place for readers who do not want to read the blog regularly.

(I think the same approach could work for LW, to make "Main" the subset of "Discussion", but I don't know how much work this would be technically.)