There's probably a lot of reasons that these cars were not a big sales success when new, but in my opinion the biggest factor was the misunderstood Mercedes/Chrysler "hybrid" nature of the car. To me, the Crossfire was the best looking car of it's type on the market at the time (meaning small, 2-seaters like the Miata, BMW X3, Mercedes SLK, etc) and should have been a great sales success......but for some reason it was not and some folks got one heck of a bargain on new ones.
But, in my opinion, the cars have probably bottomed out now in their depreciation cycle, and their good looks, uniqueness, rarity, and strange pedigree will probably turn them into a future collectable....especially nice, original, well maintained examples! I think that grabbing one of these at this time is a great move, probably with the SRT's leading the pack. But even if they remain an obscure, orphan vehicle, they will always have a cult-like following!