An interesting topic and a more exciting investment than shares/art/property for the petrol head.
Unfortunately, there are running costs to take into consideration unless you really want to dry store, which can result in perished rubber, belts, seals, tyres and so on.
Therefore the most useful option is to find a car, which you can enjoy on weekends/special occasions and sell for the same or more than the purchase price.
A good example is the Porsche 964 RS. Value’s have tripled since they were £20k only a few years ago. I’ve even seen one on the market at over £100k and these are still usable cars.
Going up quite a few levels, it wasn’t that long ago that a Ferrari F40 could be had for £150k, now they are closer to half a million. The 250 GTO that sold for circa £20 million this year… well, you wouldn’t want to drive that would you.
Back to usable classics and my thoughts on cars that can be used with minimal depreciation and could possibly appreciate in time:
<£5k - Porsche 944 Turbo, VW Corrado VR6
<£10k - Audi RS2, Audi Quattro but not the UR unfortunately at this price
<£15k - BMW E30 M3, Lancia Delta HF Integrale, Porsche 968 Club Sport
<£20k - Honda NSX, Mercedes SL55 AMG R230, Porsche 964 C2
<£25k - BMW M3 CSL, Porsche 993 C2
<£30k - Chevrolet Corvette Stingray, Porsche 993 C2S
<£40k - Ferrari 355, Porsche 930 Turbo
Big Money Car – Ferrari F40, Mercedes-Benz 300SL, Porsche 959
