The 'top' stuff is always going to come back.
Agreed - however, the number of collectors of classic bikes is declining, and the 'top' stuff definition becomes smaller and more exclusive. At least from my observation near Seattle, if it was mass produced (Merckx/DeRosa/Raleigh/Holdsworth/Masi/etc) the low values, even for their premier framesets, may never recover. Exclusivity of the best smaller builders holds value for a patient seller.
IMHO - DT shifters & rim brakes are viewed suspiciously as not only old, but obsolete (maybe even 'dangerous'). Sort of like the shift away from rod brakes or solid tires. Tire widths max'd out at 28mm = another significant limitation (less track bikes). E-bikes won't help the future vintage market trends either.
Still enthusiastic, but a shrinking market of even vaguely interested buyers.