What leads you believe that the your 1.8T is on its way out? Niggling problems are a fact on ALL cars, should you get a Mk2 you will probably have more. Personaly I would NEVER go to a Mk2 from an Mk4 unless money became an issue. The 1.8T is newer, smoother, more comfortable, fast enough (should you want more, nothing a remap cant fix).
All this about the Mk4 not being "iconic" is rubbish, its to new a car yet. Its still got many years untill it can even be thought about being classes in taht bracket. Correct me im wrong but 1.8T, the first Golf GTi to have a turbo in it out the factory?
These kind of choices are all down to personal opinion and what you want, I know what I would rather have and thats all I can offer.