i'd like to think they wont drop to 20's within a year, but with insurance being a bitch, increased police awareness of performance cars in general, the 15 yr old rule still undecided and compliance seemingly being difficult for under 15yr old models - i think its a difficult thing to predict.
what is obvious to me is that with the under 15yr old rule, of cars needing to be returned to stock, a nicely modded import *should* hold its value...but again thats being sceptacle...