I think the main/discussion divide is useful, for a good purpose that isn't immediately obvious if you are a long-time user, which is highlighting the best stuff that LessWrong has produced throughout its history for newcomers first. If they are hooked, then they keep reading until they exhaust the content of the lowest quality they find worthwhile. The people who read LessWrong the most are the people most interested in the stuff here, and therefore most willing to put up with lower-quality posts. Main/Discussion is meaningless to them, because they will read it either way. We don't need main to have a continuous stream of posts. In fact, the more very-high-quality posts we accumulate, the more we can raise the bar for what counts as "main" material.