Almost without exception, checking other destinations, airlines operating direct to their home base, are the cheapest - which is logical, as operating costs are reduced immensely.
Yet if you compare Air New Zealand's fare structure on the routes indicated, they are at least NZD200 more than the next most expensive.
I have travelled several times (on the clapped out 767's, with the wafer-thin, one-piece seats), and at those times the load factors were around the 75-80% mark.
My point is kev, Air New Zealand is NOT competitive wrt fares.
Their reputation (for service) isn't anything special, so why drive customers AWAY, with exorbitant ticket prices?
Perhaps the same logic that had ANZ rush in and buy Ansett (when they couldn't afford to) is the one used to determine ticket pricing!