Tricky one, I thought you were around the mark with your pricing, but clearly not.
I think one reason is that for the past few years just buying the right early 911 guaranteed strong value growth, however now that the market has stalled/slowed there will likely be no increase in value for the next few years.
So the idea of paying market value for a car doesn't make as much sense.
The idea of selling collectable Porsche at a discount to market value also doesn't appeal, but I think that's what it takes
Unless you have a new donor car lined up you would also know that whatever you buy will have more issues, take more time and cost more money than you allow to get it where you want it to be.