If you are talking about Vintage cars but the newer cars it depends. 348 and 355s seem to have stablized this summer. 456 and 550 seem to have come down.360 Modina have come down alittle and 360 Spiders the skys the limit.
One thing more. 6 speeds seem to be much more in demand then F1s. I traded in my 355B with a 6 speed it sold in a few weeks. My dealer has no 6 speeds left just F1s they seem to take much longer to sell.