Rust (boot, front guards mainly) and interior completeness/condition.. Two things to look for that will cost you in the long run. Think I've had 3x z10's and on my 5th dr30.
Soarer is more of a cruiser, usually auto, heavier, no lsd.. when you drive even a stanadard dr you know its a sports car.
Tidy Soarer prices are gaining ground in Japan, as are dr30 but we've been waiting for the flow on effect for years.