^^^ I got interrupted, but had planned to say I believe there will always be players who highly value certain vintage instruments/gear or luthier-built, custom/boutique instruments.
While the value/perceived value of those sorts of things fluctuate, of course, I think they may remain more stable than other mass-produced instruments (and goods of any kind, really.)
I'm just talking out of my rear end here, really.
But I have been playing a good long while. I remember in the 70s and 80s, buying some offshore, "budget brand" guitar or bass was a real crapshoot. Sometimes you wound up with unplayable junk.
At the same time, there were countless instruments manufactured during that period (particularly in Japan) that were excellent. The value of those has gone up considerably from what I see. For instance, old Grecos, Tokais, and other brands based on vintage Fender specs and made with considerable precision (no pun intended...) and quality components. I personally feel some of the MIJ Fender clones of the 70s and early 80s (including the early 80s MIJ Squiers) were--in general--on par with or superior to the instruments Fender USA was churning out during the same years.
You could pick up some of these clones for low money for a long time, but now many of the better MIJs of the 70s-80s have increased in value significantly.
The funny aspect of this, to me, is that back when they were being produced, many (perhaps most) players I knew and heard talking about them just rolled their eyes and said things like "Eh, that's just a Japanese copy. Gonna be junk. Can't possibly be as good as a Fender."
Now people are singing a different tune.