I used to have a celica gt (not the gt4). Just the 2.0ltr version. I know it wasnt a GT4 but I only had it as I was 18 and couldnt afford a supra. Even given the choice now I would go with the supra as it was the flagship toyota coupe from back then and to me is more special.
However you get 4 wheel drive, and they can be very tunable, and they are becoming very rare. It seems very difficult to find a good one now. So the fact that its becoming a rare car maybe a good reason to get one, especially with all the imported supras they days.
I do like GT4s and they can be very quick. I think 400bhp for a daily drive isnt out of the question, if you have the cash.
Although i love my supra now, I loved my celica gt when i had it, probably just as much, and it didnt even have a turbo. they are nice cars but good luck finding a good gt4. There are a lot of overpriced crap out there at the moment!
hope this helps, kinda:p