Stephen, typically used ALEMBICs (and most 'boutique' basses) depreciate in big percents (thank goodness for me . . .) as the costs involved are way above what a Fender or Gibson runs as costs. There's often no two alike, aside from basic shapes/templates and electronic packages. The wood costs are much higher. There's fewer employees who are much higher-skilled who do a lot of jobs.
It's easier to see these companies more in line with a stand-alone Custom Shop. And like most very-specialized products, you're dealing with a small clientele who are nerds/techies for this particular thing. And like anything else, the further you move away from the mass market, the buy-in gets steeper just as does the depreciation.
You see this is all markets. You sell one Bosendorfer for every 500 Baldwins. You move lots of point and shoots for a handful of Leicas.
Way more Sentras than GTR's. And in most cases, they depreciate: Look at a one year old Lexus 460, low miles, and you'l wonder how did it lose 30 grand that fast ?!?!
And you throw a used Series One on the wall at Guitar Center, then try and explain to Beavis or Butthead about the filters, the power supply, the five-pin cable . . . after the room quits spinning, they want a Schecter or an Ibanez or a Fender. So it's a small market, and a store will pitch it fast and cheap to move it.
As you so correctly pointed out, anything is only worth what someone is willing to pay for it. Vintage guitars are their own scene, but as I always wonder myself every time I wander through George Gruhn's, why anyone would pay that kind of money for these things is beyond me.
I'm long past that wonderment stage: They're tools. I do like them to look nice and play well. Fender is easily making the best axes they've ever made, and the Custom Shop pieces can be exceptionally fine, if you're into Fenders. There's lots of Fender-ish choices as well. In every possible permutation imaginable. Would not pay that kind of cash for an old bass, but that's just me.
The great thing, they screw together. Just like being back in shop class! I'm gonna build me a Warmoth one of these days just like I'd want. Probably depreciate fast . . . .
J o e y