All speculation, but I don't think we are going to see this trend completely reverse itself. My theory is that the pandemic has made two major changes to the guitar scene: 1 it got a lot of people interested in guitar for the first time, and 2 it got a lot of players BACK into guitar. So we have a surge in people playing guitar, plus a wane in supply/availability = current market.
When supply resumes a normal status, prices should come down in some categories but we are still left with a ton of people playing guitar that weren't before. Lots of new found inspiration. And all these people are going to start discovering the lore of vintage amps and the demand will remain, if not climb even higher for things like old Boogies and Marshalls.