To me, the fact that folks will pay up for excellent cars says the market for the top examples remains strong. Second, bear in mind that a lot of auction cars aren't as nice as they look on TV. Third, there are many reasons to sell, from asset reallocation to moving up-market (or down) to dis-satisfaction.
You can't price the top end of the market. The top 1-2% of any collectible will always be an outlier to the other 98%