Quoted from gdonovan:People with no nostalgia for the game will buy newer titles for the same money or a touch more.
Nostalgia is the key.
These are great games for people who get tired of the "shoot right ramp, shoot left ramp, rinse and repeat" gameplay. Nicely restored and tuned examples provide plenty of excitement with ball times measured in seconds, not minutes.
Nostalgia is key for some, I agree. About 20 games in my keeper collection have nostalgia for me -- games that I played in the arcade that stood out from the crowd. But I've added another 10 or so keepers that I never played or even saw in the arcade which are fantastic playing games with no nostalgia.
Plenty of younger people who grew up with 90's games are getting into 80's games and even EMs. I think once the nostalgia crowd dies off, these games will get scooped up quickly and their popularity will remain high.