There is a bubble in general, but I don't think it will be utterly devastating when it inevitably pops. If anything we need the bubble to pop to drive prices back down. (Start dying off you hoarders ) It's an expensive hobby in general, and most newcomers get scared off by the sticker shock when they search "pinball machine for sale."
The people who are most into the hobby right now are the people who benefited most when it wasn't hard to get a great game for under $500 and most A-tier games prices were topping out at $3,000. Younger generations carry a lot more debt than previous generations (student loans and such), so I'm curious what expendable income for millenials will look like in the future.
The number of young players now will have drastic ramifications in the future when there is an inevitable glut well-maintained machines. Pinball games used to be tossed out all the time; now they're taken care of like defenseless babies.
I think the number of profitable and viable locations for operating machines is dwindling and younger generations are anemic to carrying around change. It's not a competition for people's money; it's a competition for people's attention. Getting games in front of people is more difficult than ever before, and there is a fine balancing act of making games appeal to all skill levels.