The 4 door 2002 Explorer is just as rare as the 2 door...remember, the 5 speed manual was "standard" in 2002 no matter if it was a 2 door or a 4 door, the automatic was always "optional", the dealer charged an extra $895 for automatic in that year. Albeit there probably weren't as many 2002 4 door manuals as automatics just because most people wanted the auto, but for those working on a budget, a 5 speed manual was a cheaper option. As it stands, there is likely a market for them from enthusiasts who understand that there aren't as many around as there are automatics, as well as a market for people wanting an SUV with a 5 speed because it may be cheaper, and certainly better on gas mileage than an automatic.
Are they really "rare"? Well, in my opinion not really. They are still a fairly new vehicle, and as time passes and more and more end up off the road (ie scrapyard or pressed into tuna cans), then they may become more rare....but to be able to turn up a handful in a nationwide search isn't what I would really call "rare" in a car sense.
Are they a cool thing to own. Definitely. I'd much rather have a manual tranny in mine. Not only because I just prefer driving a stick, but also because it would keep the wife out of the driver's seat