Nice toy.
I would stick with small bumpers. For some reason if you stick big bumpers on anything with a number plate older than G, it just looks wrong (to me at least) and doesn't look quite the same as a genuine post-90 big bumper model.
Besides which, there are fewer original pre-89/90 small bumper GTIs left. So if you can keep it original, do it.
That said, I would want to lower it with some nice rims, (nothing larger than 15inch though) and a tasteful exhaust.