So where have all these vintage basses gone? I would hazard that very few have been destroyed - 90% are still out there somewhere - like old golf clubs sitting in the back of a cupboard, the loft or garage. Not ideal locations but it isn't as if they've fallen off the planet.
The rarity aspect doesn't cut it with me - they'll turn up at some point with a seller who has great expectations for an instrument that hasn't been looked after for many years.