The Mk4 GTI had several engine options:
2.0 (8valve I think) under-powered, around 115bhp, non-turbo
1.8 20valve, 125bhp non-turbo
1.8T 180bhp (found in early 3rd and 5dr Mk4's, then replaced by the 150bhp model, so 180bhp only found in the 3dr Anniversary)
1.8T 150bhp (most common)
2.3 V5 150bhp
2.3 V5 170bhp
2.8 V6 204bhp (only as the 4Motion, 4wd)
3.2 V6 237bhp (R32)
The 1.8T is a fine engine, with plenty of performance parts available and tuning is easy enough. A remap should get you to 200bhp easy.
Not all of them came with Recaros, but the standard GTI seats are pretty decent anyway.
Never heard much about dump valves on the VW scene, though i recon they're a bigger deal on the Ford and Pug scenes.
I've not seen any quad headlight conversions for the Mk4 (there are plenty for the Mk3), but I don't think they'd suit the car. Though there might be some around. Angel eyes seem to be popular though.
Hope that helps. Try asking in the Mk4 section, as some people may not check the Newbie section as much.