CAT driver training day I did was tremendous....really loved it and learned tons. Like yourself I have not tracked the GTR yet other than a quick outing a Brunters. I will be reducing the boost on mine to stage one levels when out on track as it's more than quick enough at that level until my talent increases.
Think the tranny cooler will be a must. I have also just done the anti roll bars which have made a really positive difference. The AP with XP12 combo on the brakes are all the stopping force I think I will ever need.
Better suspension and brakes with some tuition are the best mods for trackdays. Power is useless without the skills.
2010 DMG Premium R35 - SVM 650R (Terminator) - ID1000 Injectors, GTC Wrapped Downpipes, Whifbitz 102mm Exhaust, SVM / GTC Intakes (K&N Filters), SVM Bumper Intakes, SVM Bov's, SVM / GTC Intercooler Pipe Kit, SRD Intercooler, GTC Rear Light Kit, VM Gloss Black Wheels, NIS006 & GTC Custom tune, AP Discs, Carbotech Pads, Eibach ARB's, Dodson Circlips, Gotboost Extinguisher Mount, Rexspeed Carbon Exhaust tips, Mines Steering Wheel, Endless Bonnet Ram Mod