Plenty of good avice here already, but this bit particulary struck home with me. Find and arcade and go play. Then be patient. If you are patient and don't overpay, it is unlikely that you won't be able to get out from under the table for at least what you paid for it.

I am an naturally impulsive person when it comes to acquisitions. I have acquired two machines without having played them first. Both are no longer with me and one lasted less than a month. I was able to sell both for more than I paid. And, other than a few exceptions, if you (1) don't see it available today or (2) you miss out on one because someone else got it first don't worry - another will pop up relatively soon.