i think i can shed some real light on this subject,
i had a mkiv supra N/A and it had lots of carbon etc on it, fair enough it would just keep up with a GTT and get it's ass kicked by a GTR, however i really wanted a TT supra and no matter how many mods i carried out on the N/A it just diddnt have the go to match the looks
so id say keep the 33 mate, if you go to the GTT you will prob be happy for a short time then you will start to want the GTR power and handling again then you will have to sell it to get another GTR
as said previously tart up the GTR a bit and that will bring the looks up a bit and settle with that till you can afford the 34
i really wanted a 34 too but cant afford it ATM but have a 33GTR and going to a single turbo to keep me happy

keep the 33 mate you will regret the GTT