For a car that rough to reach 63% of it's value may be just that someone got caught up in a bidding war, or they just have more money than they know what to do with.
I think restoring the underside and mechanicals (and I suppose at least SOME of the interior -- like the seats) is not doing the car justice. If it were a rat rod or hot rod, maybe, but it's not. Restore the thing to it's former glory!
An interesting side note: The Pantera killed the AMX III. AMC execs were going to make a limited run of 50 or so AMX III models. Then Ford dealers got the Pantera. The AMX III was similar, but would cost a lot more. AMC execs decided to not produce the AMX III, as even at the high price they would need to sell at it would have been a money loser, and since you could get a similar car (two seater, mid engine V-8, Italian style) from Ford for a good bit less, they just didn't think they could sell 50 a year for 3-4 years.