Neil the simple fact neil you have spent time, money and effort with your car and took it to the strip and had traction issues, means the car is fully worth spending money to improve traction. If it wasn't worth it in your eyes, you wouldnt spend money on it.
Us NA guys buy the NA cuz we love the supra and can't initally afford to run the TT's. If your having traction then clearly improving it will give you a better time. Hammers the w58 on 300bhp or less I think it will hold out pretty well. Speak to jekyl about how well his held out at 380bhp and he wasn't afraid to abuse it.
The NA is a nippy motor. just because it isn't the faster model, does not mean its not worthey of your pennies.
Get the radials, and improve your time!