First of all the difference may be very slight. Hey it can't be more significant than the differences between the 996tt and 997tt and yet 996tt is still a hell of a car. Also if Ron is right you have a hell of an engine which the new Turbo might no longer have. Finally no matter what you buy something newer/different will come out sooner or later.
So enjoy and Porsche Turbos are legendry cars no matter what.