Heard recently that transTasman flights will be considered domestic ones soon. That means airfares will get cheaper, and lay the stage for political and economic union soon.
It is long overdue.
Canada and USA, and European union have their single-entry point system long ago.
In fact, when I travel from Wein, Austria to Lichenstein (not part of EU) 2 years ago, I also no need to show passport.
Do, next time I visit the kiwis, I can perhaps just bring driver's licence for ID.