I have that amp plus some of the TransMOS 150s, but I've put some of the 150s on consignment. I got my Gold Edition in 1996 for $400 from a co-worker. Back when it was in production it was J. Gordon Holt's favorite amp.
It's conceivable it might fetch $650 if in excellent condition. On the buyer's end, if it's in that good of a condition, he's getting a lot of amp for the money.
After VSP went out of business, there was an electronics repair shop in Ann Arbor that continued to build them for awhile. I talked to the main guy there 18 yrs ago (I don't think the shop has been around for a long time), and he felt that Parasound's HCA-2200
finally came up to the performance level of the VSP Gold Edition.
The point I'm making is that although the VSP was made in low numbers and was a good performer, there have been other affordable high performance amps that have come along since, and that probably keeps the VSP amps from climbing in value. Also, now that they're 30 years old, I've had to get all of my VSP amps fixed or recapped.