There are a few simple rules to follow and a couple of caveats to be observed before buying. Buy for pleasure, not as an investment. If you want to make money, call your broker. These can be great fun, but more expensive than rallying or tooling off to a car show or concours. Parts are cheap and available and they can be raced for relatively low bucks.
Japanese cars have almost no value as collector's cars.
Yet cheapo Japanese sporty cars like the Datsun B210 sedan or the 1600 and 2000 roadsters make great vintage racers for almost no investment. They are anvil-tough and easy to maintain. These engines are tricky to tune and expensive to maintain. Most are powered by small-block Chevrolets and therefore cheap and easy to race. People actually have fun driving old crocks without worrying about hauling home a pewter cup.