Thanks to all of you for the helpful replies. After speaking with the future Missus, she would not prefer to spend the extra time in Tahiti, so we will be moving onwards for that 9 day stretch.

Seems that these are our best options from what I understand:

~ AKL only if we rent a car. How difficult is it to rent a car and drive around? Is there enough to do within a 3-4 hour range of AKL?

~ Move around and do something as faerieloch did. Otherwise, is 4-5 days enough for something like KateCanuck proposed? How long would we need to maybe fly and see things in Wellington and/or Queenstown?

~ Go straight to MEL and spend 4 days there.

Thanks again to everyone!