Good point and can be the case; my personal experience with vintage basses and guitars is different on the whole.
I worked in vintage guitar shops in London over a span of many years. There were the odd vintage dogs, but not actually that many in ratio to those I played/sold. Like any bass, there will be some that do the rounds (like a SB Lull P Bass that was on here a few times that I took a chance on and quickly sold on!).
The vast majority were just average I.e. no ‘better’ than any other good instrument, though perhaps with a feel or mystic that draws us in. Like Clive Brown once said to me ‘People wrongly think the old ones are better, like they are made with magic pixie dust!’
The others, and fewer amount, were really outstanding, perhaps being a combo of years of use, great wood, and tons of mojo.
Just from my personal experience I really don’t think it’s just the dogs that are doing the rounds, more that people work out a vintage bass isn’t as special as they thought, or that the bass is different to what they had imagined or expected when buying with their eyes or dreams. That said, I totally get why people love the vintage vibe nonetheless.
My AVRI with a Fralin pup is just as good a player and tone as the very good and near mint ‘66 P Bass I sold when my wife needed a new car. That was my last, of many, vintage basses over the years- it just wasn’t worth the extra £s for me when we needed it back. I saw that bass passed round 3 times within 2 years but it was a great bass.
If I was wealthy I’d like another early Fender bass purely for the fun of it, but that’d be my only reason given the more than good enough quality of my AVRI and CS Fender basses.
YMMV 😊