I haven't had any real interest in buying old games for polygon-era consoles. I don't really buy old N64, PS1, Gamecube, or PS2 games. I have almost everything I want for the Gamecube and N64 and I don't have particular nostalgia for the Playstations. My handhelds don't get much love these days either even though there are some old Game Boy games I still want (like Donkey Kong). I just never get around to getting them.
The SNES is my big collection. Purchases of old SNES games became rare, not due to a lack of interest, but a lack of titles remaining that I still want to get. And most of those are obscure and expensive, though there are a few "huh?" omissions like Super Mario Kart that for whatever reason I have never bothered to pick up. Though I did start a thread about a recent awesome SNES pick up I did find.
I got a Genesis to start a second 16-bit collection but it honestly is not turning my crank. A few months ago I finally got an NES and that has become a new collection (or obsession) very quickly. I seem to be buying at least one NES game a week and I would probably be scared to tally up how much I've spent. The only real problems are that the games are clearly more dated then SNES titles and the damn NES is a huge bugger to get working. My brother has opened up the system twice now to perform repairs and even then it remains finicky. Funny how Nintendo is so known for hardware reliability now when their first console is easily the most faulty cartridge system ever. It's very jarring consider the SNES is an industructible brick and every game I buy for it just works like that.