For an eyeglasses wearer such as myself, I always thought Nikon's Pro/semi-pro viewfinders were the best; the FG-20 wasnt that great. The FE2 was OK, the F801s was excellent (reputedly based on the F3HP design), but the F5 was just in a league of its own. I'd imagine the F4/F90 to be similar, respectively.
Id have no hesitation in buying a brassy F3, but at the same time I wouldn't be heartbroken if it did break. Id probably just buy another brassy model and see how long that lasts - though at the rate I shoot quite a while probably.