I've almost certainly go too many books, but for me RPG books are two things:
- Something I do or plan to use the actual contents of. Whether that be rules, tools, or adventures.
- Physical objects that are nice to look at and hold.
Happily the indie RPG scene is very good at making books that cover both of those categies. I will once in a while go through the collection and give away books that I both don't think I'll ever use, and also aren't nice enough as objects to be worth keeping around.
I also have a number of magazine bins filled with zines, which I love but also desperately needs to be pared down.
Also because I will take any opportunity to share a shelfie:
Desk RPG shelf of "close to hand" stuff (and also tall books because they don't fit on the other shelves).
Ancillary bookshelf of RPG stuff: