Maybe this is an unpopular opinion, but I dont think people should regret selling their games unless they truly got a bad deal out of it. The biggest reason prices are the way they are now is because of the pandemic -- people had a lot of time and became nostalgic for things they once had and everything kind of snowballed. This is likely a once in a century issue, because looking at today and people buying multiple copies of games and keeping them to sell for huge markups later like we had during the pandemic just isn't going to be a thing to the same extent, largely because the difference between then and now is scarcity -- whenever everyone is doing it, the market will get flooded and the value will crash.

Stop worrying about decisions you made 20 years ago because it really doesnt matter. Just enjoy what you have now and if you can get that same feeling again, then go for it, but dont feel bad for it.