Generally, a car's depreciation curve hits bottom after 15 years - sometimes sooner, sometimes later. Most of the depreciation occurs within the first three years when a car's value is halved. The devaluation that occurs between, say, ten and 20 years of age is generally between 10 per cent and 20 per cent (of its initial purchase price). High-performance models aren't immune to this curve, although owners might not lose as much money. In the case of the BMW M3 (E93), the V8 sold for more than £50,000, and is now available to buy for £17,000 - £20,000. So you if you buy one now, you may see values hold steady or dip slightly - but value fluctuation should be limited. Do remember, though, that once cars pass the ten-year mark, the amount of money required to keep them on the road continues to increase at a high rate, which is where high-performance models can sting you because parts are often more expensive (this is true also of consumables, such as tyres).