I have had this happen in other hobbies. The difference, IMO, with pinball machines versus other hobbies is the cost/space issue. If you don't play online games or go to the gym or whatever your hobby is, it isn't that big of a deal. If you burn out on pinball you not only have money tied up but you get to see it everyday and it takes up so much room.

It's very normal to need a break from something from time to time. Other things in life will take priority or you may find another great hobby. If you can afford to keep the machines I would do that. If it turns out you never get the pinball bug again then sell.