Allow me to chime in here -- I own a large BGE, and while I'm no evangelist, I do love the thing a lot.
Low and slow is in fact where the Egg excels. It's true, you can crank it to 800 degrees, but it is first and foremost a smoker. There are several reasons for this -- the shape, the thick ceramic, the firebox design, but especially the very fine airflow controls on top and bottom.
I've smoked on a Weber, and a barrel-style smoker, and you can get great results. But nothing is easier to maintain at a constant temperature than an Egg. And it's really efficient with fuel; this past weekend I smoked a pork butt for 14 hours and didn't even burn through half my load of lump.
Do you need it? No. A skilled pitmaster can get great results from a hole in the ground. But does it work? Yes. And it's a hell of a lot of fun to play with, and good-looking, besides. Worth it? Well....my battered '96 Tercel gets me to work and back, but some folks like to drive Cadillacs. Are they wrong?
One word of warning: if you get one, not only are you going to spend a ton on the Egg, but you will suffer for the rest of your life with the temptation to buy an almost unlimited supply of accessories. Right now I am trying to decide whether a computer-controlled temperature and fan system would get me divorced or not; and there's some very interesting cooking stones over at that website....