I'm surprised - aren't AU & NZ super close culturally and aligned politically? I would have thought the US, CA, et al would be vying for a distant second.
Not only close, but NZ was originally slated to join Australia and is indeed named in the original Australian Constitution (that created federation) as one of the original 7 states.
NZ isn't big enough to think about. Don't tell them because they get very upset.
Australians and New Zelalanders don't need a visa to travel either way.
In NZ, I approached the immigration desk with my American partner at the time, they stamped her passport with a visa but said to me I didn't need one.
NZ is always the correct answer but is rarely given because it's taken for granted.