I bought a Renault Megane import from a main dealer a couple of years ago, when i went to part exchange it the value was a lot lower due to it being an import, paid £13500 for it, less than 3 years later i was offered £4500 part ex max, going down to £3500, with 12500 miles on the clock, the sales guy's were putting this down to it being an import ? I was not completley convinced by that but i do think an import will have a lower resale value than a UK registered car.
I also had to declare it as an import to my insurance company, even though it was full uk spec.
Another thing that was affected was mandatory call backs, basicaly i never received a call back from Renault.
When Renault called back the Megane for updates, i had to rely on a service manager at a Renault dealership who i knew that informed me when there was a call back due, and there were many on the Megane !!
I think call backs are linked between the dealership and the DVLA, so if a car is registered outside of the UK the DVLA do not have that link with the dealership, i may be wrong here so check up on that ?
If your not making a fantastic saving then i would not bother, but thats just my opinion, going on my own past experience with imports.