theres a good r34 importer???? There all the same, its a big lucky dip, sometimes good and sometimes bad, if they do get a bad car comming in, they arn't going to send it back. On the whole the guys mentioned bring in decent conditioned cars but keep an open mind.
Ive heard good and bad stories from all the companies mentioned above (some are from prsonal experience and others are from friends and other forum threads dedicated to good/bad experiences with these guys). Don't worry too much about the dealer, look more for how the car drives, how it sounds, how it feels.
At the end of the day they are used car dealers and will peddle anything that they are stuck with, so really you should go out and see these guys ,but cut out the crap that comes from their mouths and make your own decision. Warrantees are not worth the paper they are written on, and have plenty of extra cash lying around incase something stuffs up on your 10 or 11 year old r34, like a clutch is the main culprit, no one knows how long the clutch will last if they dont know the history, and they arnt cheap to replace.
If i were you i'd find cars forsale on SAU forum, then you have a history of what people have done to their cars, already published online, you can see if they maintain it, how they drive it, if its had any problems or any upcomming problems..... you can also talk to forum members who may know of the car and give feedback about it.
goodluck
End of the day keep an open mind, ignore what the dealers say, always haggle the price down, if you get a decent saving from excluding a warrantee then do that because they will fight tooth and nail to avoid a warantee job, besides they dont cover, tyres, belts, transmission, clutch ect..... and these are things that usually go wrong on the car. RB engines themselves are pretty reliable, everything else you can test the car to feel if it will have a problem later down the track (well atleast reduce the risk of buying a lemon).