I don't even think it's a supply and demand thing so much as a perception of value thing. It's like an unknown work of art selling for a hundred grand, suddenly every other work of art by the same artist is worth a hundred grand, purely because of perception. Items create value based on what people think they're worth, and while ever more than one person perceives something to be of a certain value, it will actually drive the price up. I find it particularly daft where guitars and basses are concerned. Like all technology the manufacturing of guitars has improved massively over the past 50 years. I would even argue that you can probably buy a "better" (I know, better is subjective) instrument for £3-£400 than spending 4 grand on an old Fender. I must admit I've never been a Fender fan anyway. I find them extremely bland and unbelievably overpriced for what they are. I'd rather have something like an ibanez or Yamaha any day regardless of value, but that's just down to personal taste. Either way I'd certainly take a new bass over an old one. It's like buying a Betamax video rather than a modern home cinema system just because you enjoyed a certain film on Betamax 40 years ago. I just don't get it.
Having said that, I totally get the "I've worked hard, I want it so I'm buying it attitude." So fair play if it's your thing and you want one, then why the hell not.