I only collect for one system (N64) and it is multi-fold. Nostalgia for myself, and a want to share that with my kids - it's the system I grew up on and have the most memories of.
I long ago got rid of stuff I won't play - RPG's, strategy, sim's, etc. I think I own (1) RPG at this point (Fire Emblem for GCN). I consider some stuff mine, as in, I bought it, but it's mostly played by my kids (Wii, WiiU, DS/3DS)
I don't emulate, just don't enjoy it, but i've pared down my games to games I play, or my kids play.
8 PS3
11 360
17 DC-J
60 SAT-J (about half of these are "rentals" that i'll unload after a 1-year SAT-J exploration we are doing on another forum)
47 AES
67 MVS
15 PGM
5 PGM2
2 ATOMIS
11 CPS2
13 PCB
29 Wii
50-60 GCN
180 N64
45 DS/3DS
32 Wii
6 Wii U
I have Zero games from other libraries - no GEN, GBA, PSP, NGCD, NGPC, oxBox, SNES, NES, PCE, PC, PS1, PS2, ATARI, or other.