I have a mk3 3 dr. I have a strut brace and lowered PSS coilovers. Tis very nice setup for around the ?700 mark. Makes alot of difference or did on mine anyway.
However...
There is a counter argument which i didn't consider until after i had done mine, which may have made me reconsider.
My mate had the same car, same set up. We did em at the same time. Of course we all know we are the best drivers in the world and like my mate we thought we would never hurt either of the beautifull machines we had created! Then one day... accidents do happen... My mate drives his into a telegraph pole at 25mph while adjusting the stereo. He's not goin that fast and this would have caused alot of damage to the offside wing but nothing irrepairable. BUT, because the car was as stiff as an iron bar the car was totalled.
VW don't build their cars with strut braces for a very good reason. They eliminate the crumple zones almost entirely. It my mates example all the force of the 25mph crash went up the sides of the car and folded the roof in. You have never seen anything like it.
Of course it goes without saying. My car is still the same set up and this will never happen to me, but it goes to show accidents do happen and i would have never thought of the difference stiffening up your car would make in an accident situation.