Why you want it: Because it's a Defender, that's why. It's one of just a handful of vehicles that a) hasn't changed much in over a half-century, and b) can -- and has -- gone just about anywhere on Earth. A vintage Defender (or Series I, II, or III, depending on year), especially one with the right patina, just has a presence about it that's second to none.
Why you shouldn't buy it: A geriatric Land Rover is kind of the poster child for reliability woes. It might be capable of climbing mountains, but only if it starts in the morning. A properly restored Defender is another story altogether, since there are companies, like Arkonik and East Coast Defender, that can take care of some of the deficiencies and give you exactly what you want -- but by that point, the Defender isn't exactly cheap.