When I first began collecting I was more or less a vacuum collector where I bought pretty much anything and everything I could get my hands on for a good deal that wasn't a sports game or something else that looked incredibly unappealing to me. The common thread however was the game had to be something I could see myself playing someday, although I did deviate from this occasionally if I came across a rare game.
The longer I've been collecting though, the more focused I've become as a collector. For example, back in 2012 (aka when this thread was created lol) I really wanted systems like the Neo Geo AES, Phillips CDi, 3DO, and Jaguar, along with several other odd, obscure consoles. Now, however, I've essentially resigned to ever owning these systems mostly because they don't interest me like they used to, but also because the consoles and games for them are so expensive and rare that it would be far too much trouble to get involved with collecting on those systems.
This focus has also resulted in me actually selling off a great deal of games that at one time I was really into, at least from a collector standpoint. For example, I was JRPG obsessed for the first 4 or 5 years I collected, however I've come to terms with the fact that I'm not the diehard JRPG fan I was in the early 2000s. As a result I've sold off a decent amount of my JRPG collection on certain consoles. I still have almost all the JRPGs I've collected on the SNES, PS1, Dreamcast, and PS2, but I pared down a lot of the newer ones quite a bit in recent years. I've also sold off a lot of retro games I had as well, knowing that beyond being retro, I didn't have a ton of interest in them. No console was hit harder by this than the NES, which is about a tenth the size it was at its peak about 6-years ago.
Right now, I'm sitting on most the games I've ever wanted on most of the consoles I've ever cared to own or play. My active collecting efforts are mostly focused on newer consoles like the Switch and PS4, however I'm also still collecting pretty heavily for the Saturn (both JP and US games) as well as trying to get CIB copies of SNES, Genesis, and N64 games, especially for the latter.