Hi Amanda,I lived in Auckland in the late 80s and early 90s. I remember a road trip from Cape Reinga to Rotorua. Back then, there were no smartphones or google maps to help us navigate the roads.To answer your question about the halfway point, and a place to stay for a night, I suggest Whangarei. Stay at the Lodge Bordeaux or Bella Vista Motel. Whangarei is about 3.5 hours to Cape Reinga, and 4.5 hours from Waihi.Hope this info helps.