It's a nice, well-built cab but I do have to agree $4,500 might be a bit of a reach of an asking price for a couple of reasons.
1) Just rifling through the Hammacher Schlemmer catalog, they're selling an Arcade Legends 100 Game system for $3,700 (plus $200 shipping). Yes, your machine has the potential for more games but you can't legally leave the ROMs in there, so I will assume they aren't included for sake of argument. So for the non-technically inclined in the market for an upright machine (read: people who wouldn't build their own or know where to begin getting ROMs and configuring), they would probably go for the mass-marketed machine with the no-hassle software that's a few hundred dollars (after shipping and taxes) cheaper.
By the way, reviews of these professionally built multi-game machines are immaterial considering the targeted buyer. Also, while it might be a bit unfair to compare the two given what's inside uprightbass's box, but I'm assuming interested parties would be looking for an "arcade machine" and not so much a top-of-the-line computer/display.
2) To again compare it to cheaper mass-produced cabs for the niche home game room market, you have a couple of design decisions that fair poorly: exposed trackball-plate, excessive buttons and angled controls that are parallel to neither the monitor nor the curve of the front of the panel. Despite my opinions of them, they are not big, crippling problems for your own personally built machine. When competing with other available options, however, they do stand out as flaws.
But, seriously, it's a good looking machine with some sick hardware (you might actually have better results selling the computer, monitor, et. al. separately). The design is solid and it looks like it was put together very well. Hopefully I'm wrong about the price tag being too high. Keep us posted.
Edit: Grammar