I respectively disagree; the low number rare special cars will retain value because they will be traded around like art; however over time all the rest will begin to depreciate as the potential buyer pool changes generations; the well done restomods will increase to a point because they can be used, don't need a mechanic on speed dial and will use relatively common parts. As I noted earlier, it will not be very long when the majority of "car guys" will not understand how to work on a carb, will not have the patience for the temperament of an older engine, nor the acceptance for mediocre handling and braking.
I love these cars as much as anyone, but the future is in EFI, good brakes and trouble free electrical systems.