afaik, on the technical side, that stuff is not something vbulletin supports, and it sort of doesn't make sense. I don't want my thread subscriptions spammed every time someone edits a typo... I can usually read through the typos because I'm a human and have a fully-functional semantic context-matching system. I expect most people are probably in the same boat, although they may have a different usage pattern.

If you make a post and then come up with something else interesting to say on the topic a couple days later, but nobody's posted in the thread since then, I wouldn't fault you for double-posting. It's mostly contentless double-posts and pointlessly fast ones that annoy me personally. So like, if you write something and come back 5 minutes later with something else, you should edit instead of reposting and not worry about the 3 people who might have seen the thread since you actually made your last foray into the thread. The longer the time that passes and the more unrelated the two posts, the more acceptable a double-post becomes.

This is somewhat why I advocate following the "spirit of the law" rather than the "letter of the law".