I think the V35 with a subtle kit and nice rims is pure bling. But comparing it an R34GTT is like comparing apples and oranges. It's more similar to the 350z IMHO.
I guess you have to decide on what sort of car you really want. If you're looking for more power than the GTT would give you more options locally. Plus, its a lot cheaper to squeeze more power out of the GTT than the V35. You can buy bolt on turbo kits/superchargers for the V35 but the kits aren't cheap and the NA engine is not designed for much boost.
Another thing worth considering is the fact that the V35s are automatic (correct me if I'm wrong) whereas manual GTTs are everywhere. I know which one I'd rather be driving
At the end of the day it all comes down to you. Is this a project car which you only drive on the weekends or is it something you drive to work everyday, meet clients in etc but still want to have fun once in awhile? If that's the case then the V35 is probably best.
Forget about all this engine transplant etc. You'll lose a lot of money in the long run unless you're going to keep the car forever not to mention all the problems you'll encounter along the way.
That's just my 2 cents. Peace.