You guys are being harsh on this guy.
Dude I know what you want and you dont have to go out and buy a GTR first. You will probably crash the GTR and cry forever. But if you crash the RB20 then you can shrug it off then go buy a GTR or RB25 R chassis.
Here is my input.
Change your oils and coolant. Gearbox, Motor, Diff, Brake fluid, Coolant. You know your way around cars? Do it yourself, saves a shit load on labour and there is alot of handy threads on this website that will help you.
Go out and find some nice wheels that you like. Slap on some good rubber. ie. no Nankangs
Lower it with some coilovers. Second hand or brand new depending on budget. But second hand always poses a threat to be shitty.
Does the car stop good? Or you reckon it could stop better? Check and replace brake pads if necessary.
Bump the boost up. RB20 ecu is easy and cheap to tune.
That will keep you busy and you will enjoy it until you get bored and want something that has more potential.