If you are truely worried that you might lose $500 or $1000 in a number of years eventhough you will have tons of fun over those years, you shouldn't be buying pinball machines at all.
I have yet to play TS but I know that it's one of the most highly regarded and lowest priced games you can get. As well, lower priced games hold their value more than higher priced games so my guess would be that TS is less risky than most titles you could buy out there. But don't even think of using the word "investment" because there are no guarantees that any market will just continue indefinitely in the same way.
Another point is that if you had to sell it would be much easier to do so than most titles out there because it's lower priced and highly sought after.
Pinball is the least risky luxury purchase you can make so I say go for it.
Wait, there is one larger risk I forgot to mention - you might love it so much that you won't stop buying them