One thing that GOG does that I really like is that they release updates to really old games. Master of Magic, which is just Civ 2 but with wizards, comes with a big overhaul that adds some modern stuff like a diplomacy screen and rebalances the whole game. It's incredibly fun. There's also the Unity version of Daggerfall, which I haven't played but it's cool that they did it. I know most of those things are just mods made by other people but the fact that I can give them 3 dollars and they'll package it up without me having to fight with it is well worth it.
I don't know how those people that do the mods get paid for it, if they do at all, but I'd really like to see GOG lean harder into that. For example, there's a guy, dfortaeGameReviews, who streams to like 10 people and is overhauling all of the old SSI Gold Box games. He's adding every small OD&D option and rule he can find. Getting his shit installed is a pain in the ass, he has no manual or explanation about how anything works as far as I can tell so I'd have to find PDFs of Unearthed Arcana to begin to figure out what he's done, but all the stuff he has managed to include in Pool of Radiance is incredible. If GOG could clean all of of that up I would gladly pay them and dfortae a few dollars to do so.