RPGs and Shoot em ups age well.
Perhaps it's just nostalgia talking here, but I honestly don't feel that technology and time have been very kind to these two particular genres. I realize that Cave and Touhou games have their audiences, but modern shooters feel like a giant mess to me. I can't even enjoy looking at the screen as they are generally covered so liberall-y with projectiles that I can't make sense of anything.
Meanwhile, RPGs are a genre that I just can't play on systems from about PS2 onward. I still love 8, 16, 32 bit RPGs but most RPGs made in more modern times simply irritate me more and more. At some point during, say, the 32 bit era it became the vogue thing for the story sequences to become longer, more involved, and (to me) way worse.
I can boot up old favorites or find new-to-me games from the era in these two genres and have an enjoyable experience. That being said the more recent Final Fantasy, Tales, Star Ocean, etc I just can't enjoy them the same way. There are exceptions of course. Yeah, they're both a bit old by this point but I thought Gradius 5 was fantastic and likewise for Dragonquest 9. I guess my point is these two genres work just as well on older hardware and for that reason prices have gone up or at least stayed relatively consistently high. Sometimes there's just no need for an upgrade when what you've got is perfectly serviceable.