As far as AA goes they are pretty good, however seroius problems usally cant be seen without opening up the engine or thereforth. The AA should be able to spot major problems or advise of the overall condition from a general degree.
The AA down here in hamilton have been decent in previous years. usually you should be alright, its with fresh imports that a problem can come down the track and unnoticable with 1st inspections.
The only people ive heard talking about the AA not being so good is Aucklanders, but I have to question their inspections aswell but as previously said, without taking stuff to parts you cannot guarentte no problems.
However a good mechanic should be able to listen to engine noises, test drive the car for any obvious wear and tear and visually inspect for any concerns.
my 1 cent worth...........Hayden