Jap spec S15 Spec R's had a leather steering wheel, rear window wiper (as mentioned above), no rear bumper reflectors (Aussie spec ones needed them to be ADR compliant, pity, as they wrecked the lines of the rear bumper), standard A-pillar boost gauge, and in-dash TV's as an option, different badging (Silvia instead of 200SX), along with other minor stuff.
The Jap spec S15 R's had the same sized T28 turbo, but with ball bearings (slightly faster spool up), ECU tuned for better fuel, and a different stock exhaust system (not fully sure on that). Because of these changes, the Jap spec R's put out 184kw, 37kw more than our Aussie specs.
Just a sidenote: The Jap spec S15 Spec S's were non-turbo with a 5-speed gearbox instead of the Spec R's 6-speed, and a 4-speed auto as an option. These put out 118kw and had different wheels
Also: The Jap spec's badged with Aero just have a sideskirts and a rear wing (sort of like the Spec S/R GT's Nissan Australia produced to clear the remaining cars)
Edit: Damn, beaten