I think the two reasons you listed are probably the two biggest reasons people like to buy retro games, but a lot of retro gamers are just content owning and playing something retro that they haven't played before. Retro games are very different from most modern games, and players who enjoy them prefer them because they offer gameplay, design, attention to detail, music, and art that's mostly absent from modern games. I'm now collecting Sega Saturn games, and I never even played a Sega Saturn until this year. And while there are a lot of games that are expensive on the system, there are a lot of excellent, affordable games, as well.