The 914 hits the perfect balance between being old enough to be a classic and modern enough to be realistic for everyday use. Mine starts right up on the first twist of the key, even after sitting 2 or more weeks in cold weather (it's fuel injected), and the wide interior and two trunks make it practical and comfortable.
It's not fast, but it's quick enough, and the steering and handling really keep you involved in the driving experience. It shifts and brakes like a 32+ year old car, which means that even when everything is working right, it still takes a little skill and care to drive it smoothly. In other words, it's no modern SUV, and for that I love it.
Of course, it helps if you're handy and have some garage space and a little extra money for the inevitable replacement parts. Some parts (especially cosmetic stuff) can be expensive, but most of the parts you need to keep it running are pretty reasonably priced. Buy the best car you can afford; if you have to fly a thousand miles to find a better 914, consider your plane ticket money well spent if it gets you a better-running, better-looking car.
Some people advise having an expert look the car over before buying. By all means, inspect it carefully, maybe take a motorhead buddy along too, but in my opinion, at the 914's price point, a professional look-over isn't necessary unless the car is priced way over market value. If you're considering a car this old, you probably know what to look for in old cars anyway, and the 914 is a simple car; beyond rust, there's not a whole lot of hidden surprises that can really bite you. And if you do have trouble or questions, there's plenty of support on-line and replacement parts are ridiculously easy to find.
If you're looking for an affordable, reliable classic that's not overpriced and/or overrated like some classic sports cars I could name, you need to have a look at the 914.