You can pick up a low mileage Roller for the cost of a new hatchback. Drop a diesel in it and you’re good to go. 🙂
Morris Marinas are going to be worth money purely because those that didn’t rust away were destroyed by falling pianos, so rarity value will be high, and you’ll be able to hire it out for movies.
I think any of the low volume British cars that had fibreglass bodies would be a good buy. Usually there’s an owners club, so body parts are easily sourced, and their consumable mechanical parts are from mass production cars, so also easily sourced.
A car I would consider is the Smart Roadsters. In 10 years time we may have to sell a kidney for fuel, so small engines will be in greater demand, and the mechanical parts are still being made for the normal Smart cars.