It's the same thing that I've been watching for a while now... the top end drives the lower end higher, and the cycle kind of repeats. Those nicely restored games that go for $10k make this game look like it is very reasonable at $6850ish to some people. Yeah, it could use new decals and a new playfield - although really, that playfield isn't half as bad as a lot of them that I have seen - but that is $1500ish and some work. So, for $8500ish and time, you suddenly have a game that people are asking $10k-$11k for.
It used to be that if you bought a $2500 game that was blown out for $2000, put in a new playfield and fixed it up at a cost of $1200 to you, you'd end up selling it for maybe $2600 or so because those upgrades just weren't that valuable to people. Now, sellers are expecting to get $2000+$1200+$800 for time+$1000 because you had it for a year for games... and in a lot of cases, they are.
It never ceases to amaze me how whenever there is a Stern bashing thread on here that someone brings up how "only a few of their games appreciated in price immediately." These prices are being driven by people who want to get more out of every machine that they put into them, and a market that no longer has much of a source for blown out titles. Agree to pay the higher prices... or look for lower priced titles.