I never "complete" any collection, but if I did it wouldn't be a video game collection. There are too many bad games out there. I'm not going to spend any money or devote any space to games that are shit. I have too may other hobbies, other passions. Rather than pay a grand for Magical Chase I'd be traveling someplace or buying car parts.
The systems with the best good/bad ratio are probably the Neo Geo and the Neo Geo Pocket, but even those systems have a dozen or so stinkers (Gowkaiser, pachislot shite).
If I were to "complete" a video game collection it would probably be NGP, Wonderswan, or Dreamcast. It certainly wouldn't be NEC, and it sure as hell wouldn't be US NEC since the box art is f*cking horrific, and then there are those cheap-ass outer boxes, and the games that only have cheap-ass outer boxes and no case...its like collecting match books or pogs or something.
To anyone who "collects", that's fine, but make sure you are enjoying life to its fullest before you spend all your money on plastic crap you won't even play.