I suppose if some of them are rare classic games in pristine boxes with all the all the collectors' gubbins intact they might fetch a few quid on
ebay.
But yeah, what Dave said about GOG. I tried to get some old DOS/W95 Zork games to work but they were unplayable until I gave in and spent the extortionate £1.99 (or whatever. They're £4 something now) they wanted.
My son had dozens of games, maybe a hundred or more, but he solved the keep/resell question, by immediately taking them out of their cases and storing them in a pile on the floor so that now they have no resale value and only about one in ten can even be read by a DVD drive.