With regards to cars and motorbikes, there are lots of people who enjoy both restoring these back to original condition and custom building enhanced versions. The price of some old cars is actually rising due to their easy re-use in other vehicles( think sierras and granadas).
It is also getting harder and harder to find classic car projects that have not yet been restored but are worth restoring. Restored classic cars are also being used as investments again.
Aircraft, other than a few vintage types do not have that really. Even if they did it would only be a labour of love for an owner and not be financially viable.
With only a limited amount of pilots and numbers falling the old types probably should be allowed to retire and we should be embracing the new types. There is just not enough people in aviation to justify keeping old relics in the air. I would rather see small businesses based on new technologies being given the support to grow.