It seems to me that there are some people who shy away from imports simply because it's an import but they don't really have a good reason why. There are rules and paperwork to make an auction legit the same as in this country and you are no more at risk than you are buying a UK car from a private seller. If you want the same spec as a UK GT car you can get it, you can also find you may get unexpected optional extras. The base model in japan does have 17 inch wheels but the others have 18's as standard. I can't see the problem with servicing - get it serviced where you like - if you want Nissan history then go there.
When I bought my car I had cash in my pocket but purposefully went down the import route as all I could get at the time was silver or gun metal which I didn't want. It was a nerve wracking experience but when I saw my car with 5k miles on it and immaculate I knew I'd made the right decision. I got the car cheaper and will sell it cheaper. The only thing that was disappointing was that it had lots of really hi tech aftermarket stuff I can't use - TV, Sat Nav, DVD etc - I got a new unit for xmas which is going in soon.
My advice would be to simply go for the best car and stop sweating over whether it's uk or jap.