There are plenty of reasons why the Mazda MX-5 is the best-selling sportscar of all time; the key ones are the affordability, reliability and brilliant driving experience that it serves up. Such popularity ensures a steady supply of used cars, many of which are special editions. There have been at least two dozen of these, and they're invariably worth no more than standard cars. Don't dismiss 1.6-litre cars either; they're not especially quick, but they're still a blast to drive.