Yeah, and the other "flip side" of that argument is the fact that old fashioned steel is tough and pretty easy to repair and/or touch-up w/paint after it actually gets some use. Aluminum, not so much. So yes, the aluminum alloy is lighter, but more expensive and harder to fix if you actually go down.
I think it may depend on how much off-road riding you actually do, and if you are putting yourself in situations where you might dump it more often.
That said, marsbeetle, you point is very well taken. If you aren't careful, it is pretty easy to turn a bike into any overladen pig if you just keep throwing gear on without considering the total extra weight of all those farkles.
Things will always turn out good in the end. If things are not good, then it is not yet the end.