As you probably know I,ve just swapped my 166 for a GT.
The GT is not as well made as the 166 so expect to be tinkering a lot although I know you like the tinkering
look out for boot rattles, windows that don't auto lift properly, the front upper wishbone squeek. My 166 lasted 150,000 miles before the front upper wishbones needed replacing but the GT seems to need them every 30,000 miles or less according to the owners on here. Mine squeek and need doing as soon as it's driving me nuts.
Clutches go quicker than the 166 roughly 60,000 miles. It's smaller more cramped more plasticky and even more problems than the 166 but still glad I changed to the GT. I'd had the 166 for 7 years and needed a change. the diesel is a peach of an engine with more than enough pull. Expect your clutch to go very quickly if you do the remap unless you upgrade it.
I'd have done the remap already if the clutch on mine hadn't been replaced recently.
Defo go for the bose if it has it it. It's no where near as good quality as the 166 sound system due to the downward facing subs in the 166 compared to the abysmal box in the boot that the GT has but as one of the previous posters says the standard audio is rubbish.
just turn the vol up when you start the car and you won't notice the sound. Once it's up in the revs it actually sounds pretty good but not the same as V6 with a stainless.
I put £50 in mine 3 weeks ago and it still has some left. I was putting that in every week at least with the v6.
All in all I'm very happy and enjoying ragging around like a 17 year old who's just passed his test at the moment. Hopefully this feeling will last, still missing the 166 though. Will you be keeping yours or is it a replacement ?