When I started in the early '90s I didn't know anyone who purchased any pins NIB. My buddy and I would play all the latest pins at various arcades and bars and talk about which games we'd like to own. For several years I hunted down my favorites, mostly through the local distributors, and they are all keepers to me.
Along the way I did make three "opportunity" buys of games not on my must-own list:
1996 Gottleib Barb Wire (barely used) purchased in 1997 in very good condition
1994 Sega Baywatch (used) in 1996 - cabinet nicked up but playfield great and recently added ColorDMD
1997 Sega X-files (NIB) purchased in 1997 on a close-out (I still have the box)
I'd consider selling those three, but I'd rather keep them than sell them for the prices they bring. They're still pinball.