Most things that become collectable usually start off being either rare and/or fragile to start with - if they're ubiquitous and robust then they're just never going to reach big bucks, it has to be something that isn't easy to find, either because barely anyone had one or because all the originals broke.
Its pretty unusual for bass guitars to be so fragile that they deteriorate irreperably, so that leaves you with guitars that were either rare to start with, or things that were pretty unpopular so nobody bought them - until someone somewhere made a cool record with them.
I'd suggest Fender Dimension basses possibly tick that box, also the Squier 40th Anniversary models is an interesting shout but I don't think they're unique enough to ever get properly collectable.
To be honest though I think the naysayers above are correct. The number of collectors is diminishing, not growing. There will definitely be some fire sales in the next decade. Thankfully I've always bought my gear to use and not lied to myself that it's an investment.