A side comment here: I am always into gadgets and have my eyes on the Harder and Steenbeck Infinity model....but I don't really need it. Every time I convince my self to spend the money for it, I look at some incredibly painted models, which blows away anything i could ever do...all painted with a cheapo $25 single action AB by some friends on line. The bottom line is that a skilled air brusher can work magic with a cheap AB, but a low skilled air brusher (me) can't create masterpieces just because he has an expensive piece of equipment.
Another, completely contradicting opinion is that if you can afford it and you are at the level where you can make full use of a finely tuned AB, go for it. You're putting money back into the hobby and spending it on good, clean fun. You shouldn't feel bad about buying what you can comfortably afford.