No, I think there's always merit in new discussion. Perspectives and answers shift over time, so a question asked this year might have very different responders and responses 10 years from now.

Take an open question like "What is your go-to TV series/movie/game/book that you recommend?" A discussion on that topic that is 10 years old isn't as valuable as one asked today, because new media will have released and older media will be recontextualized. Even if a lot of the answers are still recommending timeless classics.

And I also wouldn't trust moderators not to be heavy-handed with posts that are "close enough" but not quite the same. A question like "How do you deal with the loss of a loved one" versus "How do you support someone going through a great loss" might seem similar, but are targeting two different purposes.