There is a fair amount of performance parts around for GTI's, more than for any other Almera anyway, all the usual stuff can be got it just takes a bit of digging compared to some of the more commonly modded cars.
Cat-back exhaust systems, backboxes, lowering springs, coilover kits, strut braces, seats, alloys, air filters, performance disks and pads, big brake kits, bodykits and all sorts of engine tuning bits and bobs can be got.
Well worth signing up to the club when you get your GTI, you'll save your membership fee in no time in advice and discounts.