Unfortunately the USA market for E bodies has been this way for quite a while. I think Barrett-Jackson/Speed visibility has had a bit to do with it in the last couple of years. But it started being an investor's market originally back in the late 80s/early 90s when investors found out they could flip an E body and make a tidy profit. Unfortunately it priced true collectors (vs collectors/investors) almost out of the market.
For that matter, you can just about match the cycling of the financial markets to muscle car prices. When the market reacts strongly (one way or the other) muscle car prices seem to go the other way mostly.
Luckily the last couple of years Mopars have not been the hot property of the investor class (Fords are currently hot) but they have started rising again this year at B-J and I believe they will hit the astronomical prices again in a couple of years that they were 5-6 years ago.
This is a good/bad situation as I see it. Due to the high prices these cars bring, there are a lot more re-pop parts out there due to folks wanting a concours restoration and willing to fork over $$$$$$$$$ to get it than there were 20 years ago. Even for mundane pieces. I remember scouring junkyards for parts for my Dodge pickups and my buddy's Cuda as no one made parts (even relatively simple parts that cross-indexed like door handles etc) for Mopars in general. So the high-profile investor is who, I believe, we have to thank for the Mopar restoration aftermarket and curse for the prices we have to pay for our Mopars. (Now hopefully they don't find out about the big C boats as I would like to have a '71 Sport Fury III. C bodies are the best deal in Mopars nowadays along with 60's & '70s D and W series).
Sorry for the hijack, forgot I was in the for Sale section