Since that aluminum MTB has been just sitting around for the most part, you probably could get many years of use out of it, most probably more than just five or six years. However, if you'd like to just make one MTB purchase, the purchase of a lifetime, then the Trek 820 would be that bike. Once you've upgraded it and perhaps later placed a spectacular fork on it, it would become peerless. Peerless and awesome!

I've had similar thoughts lately about the Giant Boulder, too! Once you've got that chromoly steel frame, suddenly the possibilities become endless. The possibilities become endless, because you have more time to make better upgrade choices.