Wow, a Carrear 4$. I love them myself. Edmunds has a good depreciation tracker, IIRC. I don't think too many people know all that much on the market of high end sports cars AFA being able to chart the future. There are so many variables and not that many cars as base. It's a little shoot from the hip, IMHO.
Two sources much better than I would be the Porshce Market Letter (I think he will talk to you one on one and is a member of the Early S registry, if not here) and Keith Martin's Sports CAr Market. I'd look for articles in back issues about Porsche.
Just as a WAG, I'm gonna say the real expensive 911's are gonna loose 10%/yr after an initial 20% hit and falling off to 5%, in VERY general terms. Any could vary. Seems like GT2 and 3's hold up better than that, maybe Turbos as well.
I can tell you that Boxsters are on the other end and I suspect Cayenne's, too. If you chart each and every model, you should get a clearer picture. It's a lot of work.
Or, you can ask here.
