I rode my military 2000 from Vegas to Tucson in two days, a very cold ride but I was surprised by how comfortable the bike was. I expected "thumper" fatigue but found the only discomfort was the cold - and the work I had to put into getting the bike started the second day.
As I've mentioned in another thread, it died as I got into Tucson and I've now stripped the head and am rebuilding the carb and cleaning the gas tank... when I'm done, I hope for some great and trouble free riding! My problem was that the previous owner clearly didn't perform needed maintenance, and the head was severly carbonized, there was rust in the tank, and the carburetor pilot jet was clogged.
I can't respond to the issue of maintenance, because I haven't had the bike that long, but I am sure that the military model is the same as all other Enfields... they are low technology bikes, and so long as you do all the regular maintenance, you shouldn't have problems. Unlike modern bikes, they dont have the same high level of design engineering going into them (with maintenance free systems), which means that you must take good care of them. But the advantage of a low technology bike is that YOU CAN do the work... it's all part of the fun of owning an Enfield.