Hi 38 Coupe
I live in Australia and have just spent 2 weeks in New Zealand motoring around the North Island.
We stayed in motels all the way and some of them were very nice but the 2 nights we spent in Napier we were at the Pebble Beach Motor Inn which is right in the city and it was the best by far of any that we stayed at. I would stay there again any time.
http://www.pebblebeach.co.nz/
The Speights Ale House is also a great place for an evening meal.
I would also echo the itinerary that swoop gave you but I would drive from Auckland to Napier through Rotorua so you can see some of the country and then leave the car there and fly out.