As a Kiss fan, I know how difficult it is to get autographs like this- Consider carrying this big piece of glass around (like a concert, for example), then trying to get them to pose for a picture while it's being signed. The thing with this glass is not only the signatures, but the ability to authenticate these signatures beyond someone just telling you they had it signed. There's no doubting the authenticity when you see pics of the guys signing it. The only thing that could have made this better is if they were in makeup.
Problem with asking on this forum is most aren't true Kiss fans, and this is a Kiss fan question, not a pinball collector question.
As a Kiss fan and pinball guy, I think this glass is over the top, but that's just me. I have a signed 1979 backglass, non-german, with Ace and Peter's signature in mint condition. The reason I don't have Gene and Paul? I haven't wanted to lug it to a concert and around a venue and risk breaking it. Imagine what it took for this guy to get this done, and the price seems like it's reasonable and perhaps you could score it for an offer.
Just my $.02.