Japanese audiophiles have rekindled the interest in valve amps and classic turntables. They are paying huge bucks to get their hands on classic amps.
As for stupid people paying huge amounts on eBay, it's not so much that alone. Most esoteric valve amps command high prices because they offer aesthetics that solid state amps lack. Chromed chassis, glass panels, high end connectors, and hand assembled/built all plays into the final cost. Sure these features don't add to the sonics of the unit; it's more of character than anything else. A Mercedez doesn't get you down the road any better than a Chevy does. But it has the class, the assembly quality, and design behind it that demands the higher price.