The added pictures definitely help, looks like a pretty decent start for a restoration.
As far as rare vs. valuable, I'd have to say the '70 and '71 GT's are fairly rare. But as far as valuable, not really. I'm surprised that the auction is already as high as it is. The Butterscotch '71 in my signature was purchased for less than what your auction is at now, and it had a complete matching numbers drivetrain, buildsheet, high impact color, and was almost 100% complete with absolutely 0 rust. Original CA car, still has the original paint on the ground side of the floorboards. Heck it ran (although badly, needs a rebuild) when I bought it.
The bronze '71 in my sig was more similar in condition to yours, 318 car with no drivetrain, rough interior (missing the front buckets), and with rust in the roof skin (although solid everywhere else). I picked it up for $800.
Don't get me wrong, I love the GT's. In '71 only about 1,255 were made, although there are no specific production #'s from the factory, just a percentage of total production. They have pretty cool options, and some interesting stories. But realistically, at least at the moment, they don't seem to be much more valuable than a non-GT from '70 or '71. That may change over time, but since most are only /6 cars, or 318's, its unlikely they'll demand big money even in the future.
