I have $12k + shipping into my nice example I purchased in March of this year. It is the family favorite. The nice thing in my mind is that if I ever do decide to sell it (not likely any time soon) it is very possible that I won't take a bath on my cash and maybe make a little. Either way, I probably won't lose as much as I would have if I put that money in a boat, for example. This money, for me, would have been simply sitting in a bank and not earning anything as part of my "disaster fund". I'm very fortunate that I earn enough that the expenditure did not hurt me financially at all.
That being said, I know many, many people are not in that financial situation. I would put MM and any other pinball on a list of totally discretionary spending (obvious) and so in my situation playing MM > money in savings earning less that 1%.
From a play standpoint, like I said, it is the family favorite and the favorite for just about anyone who comes over and doesn't know anything about pins.