I owned an AE500 and the only problem I had was dust. The damn thing was a dust magnet and the filters supplied (worthless foam) did nothing to stop dust. Soon the colors started getting "pinkish" and in the end I just sold it to a friend who could care less.
Does the AE900 have a better filter system than the 700 and the 500?
Since the Panasonics and the "Z" models for Sanyo are relatively the same in the past generations, I can say it's safe to surmise that this trend will continue with the Z4.
The only reason I am considering the Z4 is that it has been the counterpart to the Pansonic projectors for a few years now (I'm a big panasonic fan) and that the Z4 not only has an automatic lens cover, but it also has a "hepa-like" filter system AND a way to blow the dust off of the LCD's without sending it into service.
I was considering a BenQ 7700, with it's sealed light path, but I really don't want to get a BenQ with the crappy lamp that blows out prematurely and have to wait two weeks for a replacement