To be fair it all comes down to personal preferance, the style you're going for, and sometimes even the colour of your car.
My 1.4 SE was a complete GTI lookalike.. had the arches, skirts, rear spoiler, bumpers, mirrors, interior, electric windows, side mouldings, VR6 splitter, front fogs, rear lights, roof mounted aerial.. in fact the only thing it was missing was the engine lol
And to be fair, I couldn't have imagined it being without all of that stuff. The black and green theme I had going on looked awesome in my opinion.. so many people asked me if it was a GTI.. and so many people loved that car.. perhaps that's why I got 1400 quid for it.
My 1.6 has fully colour coded bumpers, no skirts, and no arches.. and I couldn't imagine it any other way either.
All I can really say is keep your eyes open in local scrapyards cus something might pop up, try ebay, or keep your eye on the classifieds on various forums.
My local scrapyard sells GTI arches for 40 quid a set.. GTI skirts for 20 quid a pair.. GTI rear spoilers for 15-20 quid depending on condition.. GTI rear lights for 30 quid a pair.. and fog lights are pretty hard to come across so normally about 30 quid a pair.