If you aren't already familiar with it, I would strongly recommend browsing the

Adventure Rider forums

They have regional sub-forums, with one for Australia, Tasmania and NZ, IIRC.

Its a bit BMW biased, but an excellent resource to find out the best and most outrageous roads in advance (like the Nevis Valley Road). Really the forum is more about destinations than any particular brand of bike. NZ is a popular destination and there are lots of trip reports, etc. in the "Ride reports and pics, pics, pics" sub-forum.

There is also somewhat of a bias toward unimproved roads, but still a ton of stuff if you want to stay on the paved roads.

If you *did* want to check out some out-of-the way stuff, you can rent a BMW R1200GS, which is made for dirt roads (not trails) from Kea Motorcycle Rental.

<jealouser>
Jim