There is no denying that the UK GT Spec is more desirable and will hold its money far better, but their are some nice JDM's out there. I have owned a Fairlady for approximately 18 months now and do not have any regrets, bought it based on its service history and modifications.We haven't had any issues regarding fault codes, all have been identifiable though our Snap-on Modis code reader - I am sure that most garages will have something similar which is capable of reading codes.
As mentioned above there are key additional extras or upgrades with the UK GT, such as Brembos, electric leather seats and electrical compatibility (SAT-NAV, Bluetooth etc). Out of the majority the only thing I would have wanted are the Brembo brakes as the JDM ones look pants, especially when you run 19's!
You will find a 'decent' JDM cheaper than a 'decent' UK GT but consider the cost of upgrading certain parts. No point in saving a grand on a JDM if you then have to spend that on Brembo's for example.