You might be right for the high end (the Bentley example), but the middle/lower end of luxury isn't that interesting as a collectible, cars like a 5 series BMW, or Lexus LS, and could really drop in value.
The supply is already gone and has been for a while. The other comment in this thread on ever-smarter (cloud connected) cars too means that the market for not-cloud-connected cars is going to continue to increase too.