Both for me..

I find i can really get stuck into fixing one up, then it might piss me off and i walk away for a while and come back with a fresh approach.
Playing is the same - ill fall in love with a game again after an absence and wont stop playing it for a few weeks.. then ill move on.. come back etc etc etc.
Best part of playing the pins is having a line up of different eras all working. It really screws with your skills moving along the line adapting to the various styles of play.
Can be reverse 2" flippers on an early 50's game straight onto 3" flippers on something like Super Mario, then to SS machine and then to impulse flippers... all feel so different... and adapting is not easy!