I don't think that there is a single answer to the question. For most people, IMO, I would have to say there is a lot of nostalgia involved and enjoyment from that. It takes you back to a happy place, especially if you had owned that system in the past. For others, I am sure it just comes down to bragging rights - "my cab can emulate a gazillion" old systems and I don't care that I have 300 iterations of Asteroids!" I would say that there is a 3rd category that enjoys the challenge of making things work, looking into the past of a system that they never used before. My primary interest is MAME, however, I have very fond memories of the early Atari and Intellivision consoles and the Atari 8-bit systems and I find them to be an enjoyable escape. I also enjoy my Xbox and Xbox 360.