How are the sales prices of older Mopars holding up?

The heart of your question may be the market value of collectibles in general. In that respect the appraised values remain pretty much unchanged. Their are confirming reports out there with subjects such as art, wines, autos, coins, etc..
If you want to buy a street rod, driver, today you'll find some good deals but if you want a showroom, display, you can expect to pay full price.