It's still a beast, both in performance and power usage, but I agree with Unknown_K in that you're buying it most likely as a collectable, as opposed to a machine that can be used for a good few years yet. If you want "that machine", you can pick up Mac Pros for a few hundred more, much more versatile units and even the 1,1 models are still decent (and cheaply upgraded to something much better).

Most Quads have died, and those that haven't been serviced/overhauled now will most likely go too. In a few years time, owning the "last, great PPC" that works will be a good collection piece.