I would only expect either NZ1/2 or 1/5 or 2/6 trip to be considered a single journey for the purpose on the status boost. These are two trips in the same direction (which is the key here).
Likewise I'd expect a single journey if you travel WLG-AKL-KKE on a single ticket but two journeys for WLG-AKL-ROT on a single ticket. If you travel WLG-NPL-AKL on two seperate tickets on the same day this will also be a single journey.
The problem as I've already mentioned is that Air NZ don't have a definition for a journey in the T&C and can't provide a definition if you ask because they can't due to the complexities of Airpoints.