I've been there multiple times, each for a month plus. Other than one work trip (setting up navigation electronics on a 60' sailing cruiser in Auckland harbor) I was on a motorcycle. I've gone from Invercargill (southernmost town) to Auckland in a day, but that was a major push - BTW, if you're on a bike, you can take the truck ferry. There are showers and sleeping quarters if you can show you're a truck driver - and not necessarily a driver of one of the trucks onboard. I think an ODIA member card would work. Otherwise, there's a comfy bar.

Anyway, I ran into quite a few people on NI who had never been to SI. The two islands are spectacularly different, although you can get a SI vibe in Urewera Nat'l Park on NI, and a NI vibe in Nelson.

When I’m there on a bike, I like to pick directions randomly at each intersection; the only thing I was trying to do was not be at the same backpackers’ two nights in a row.