IMO Pinball machine collecting is in its infancy.
I had the pleasure of visiting a fellow in Paris who had a private museum full of wood-rail machines. Probably 200.
Each in perfect restored condition. He used to be the distributor for several manufacturers back in the day when pinball was king.
I cant think of a more fun hobby than pinball collecting and cost effective as well. Each machine has its own "soul". And if you choose wisely you get all your money back when selling; A free hobby.
A three or four game collection is plenty and reasonable but there are us addicts that can never have enough.