Retrospective analysis is important; is regret? Is it crucial to have the emotional distress that comes with rational evaluation of past choices? Does negative emotional reinforcement really work at such long time remove?
So, I don't know about regret specifically, but when researchers asked people to remember instances where they felt specific emotions, and asked how strongly the emotions reoccurred during that process, the number one emotion was embarrassment. Some theorize that fear of embarrassment driven by memories of making mistakes is one of the leading factors in the fluency gap between the first and second languages of children to foreign parents (who speak English [or the language of their peers] much better than their parents native language, even when their parents don't speak English at all -- somewhat odd considering children _need_ to communicate with their parents to survive and get basic needs met).
When you're paranoid, you're worried about a bad situation without thinking through the ways you could respond to it or fix it if it does happen. If you have planned through what you will do if the worst happens, there's no way to be paranoid about it.
Similarly, it's hard to regret something if you've learned from it and recognize that you never would have learned that lesson if it hadn't happened the way it did. Growth is motivated by responding to problems, not responding to everything going well.
I don't see it as pathological -- it's not like I sit in my room sobbing over past failures. But I still feel regret and as a result am (I think) a better person.