I agree with MBS. If a game is currently available from the company itself, then I'll buy it. But we all know the used games industry is terrible, and I don't know how many of them I want to support. Whenever I try to buy an older game, it usually ends up being a fake. And since the companies won't release it, people can easily sell the game for exorbiant prices online. It isn't worth it and it doesn't actually support the gaming industry.
Also, sometimes I emulate games I already own on the go. I have Zelda 1 for the NES AND Gamecube, but if I want to play it while on campus, or a modded form (usually a randomizer), I have to emulate. But those are games I do own physical copies of, so there's no reason to keep me from emulating it in those cases.