I collect arcade machines for one reason: I enjoy playing them.
I will buy games on occasion to fix up and resell, but the motivation is not driven by profit. Generally, money made from repairs and reselling of machines is used to acquire games that I enjoy playing and working on.
Repairs of classic games is becoming difficult, if not impossible in some cases. While "standard" logic chips used in the early 80's are still available, "custom" chips that were created by the game designers aren't, and never were, available from any source other than robbing them from other game boards.