Back in the day when I did not have an annual, I always took out travel insurance just for medical in case something happened before the flight, or loss of luggage, or something yadada with the rental car.
If you are renting a car, or have bought a package, I would def consider it. Saying that, I will always have travel insurance, regardless of recip.... it even paid to have it on a domestic trip in Australia! Paid for additional costs incurred because of a medical problem, to return home.
Edit: The cost for insurance to NZ is nothing anyway , compared to "North America".... How long are you going for albatross710?