I've had an R34 GT-T, got bored of the power, plus it wasn't a GTR. So i go an R32 GTR (don't like R33s.)
Anyways, they still look pretty good on the outside, but yeah, the interior looks pretty crap as compared to the R34, but not too bad. Seats are great, just the dashboard is annoying (i recently saw this carbon fibre look paint stuff that can make ur dash look heaps newer!) Also agree about the 3 tachos in the middle, they are pretty hard to look at while driving, also, they can reflect some pretty nice sunlight into your eyes at times.
Power wise, GTR owns it, as expected, 34 has looks, outside and inside. It will feel a hell of a lot like your R33 GTST, actually, it is your R33 GTST with a few major upgrades.
So it depends do you want newer looks etc, or more power. At the end of the day, I might sell my GTR and get a GT-T again, then sell the GT-T and get a GTR! LoL. Flip a coin?