1) new engine is unlikely. SC just had transmission upgrade for 06, makes little sense to spend major money to upgrade power train again for a low volume car.
2) navigation had been upgraded either 05 0r 06 to integrate blue tooth. in terms of functionality, GS nav is not much better than the 06 nav.
3) again, unlikely for a low volume car.
4) color is likely, since it's an inexpensive upgrade.
a new sc model is probably not due until a few years later. sc is a low volume car, it's not profitable to upgrade the car often.