I maxed at 13, now have 3 and a bunch of money!
Like others, I spent too much time working on them.
Also, having less makes me appreciate going to a fellow pinsider's house to play pinball that much more.
Pinball, for me, was becoming an antisocial hobby. By reducing my collection, I now have to go out to play new games. Great bonus is you get to talk to other pinball players too.
Best regards,
Tom