My community is still small and you know well how much it takes to get people to post, but - without going back an checking exact figures - it feels like I’m editing about every other post to add a second enter for the paragraphs.
Maybe my framing of the issue in the OP was a bit misleading. My point here is not the total length of the post (although that can also be a problem) and not that people don’t care about inserting paragraphs, but that they do so incorrectly: they press only enter once. (I suppose MS Word is to “blame” here, because it by default inserts white space after CRLF to make the paragraph visible, and people are used to that.)
That’s why my suggestion was limited to identifying single occurrences of Enter with text before and after them. This would mean that the edu-notice pops up when people wrote something, hit enter once and continue writing.