What dates will you be in Auckland for? I only ask because of the Rugby World Cup. It’s on from 9 September until 23 October and may cause a little disruption to plans around Auckland.
Last time I was there I did a great scenic flight over Mt Tarawera, the Blue Lake, Lake Rotomahana etc.
We will have a full day plus a half day in Auckland. It looks like after that we will be heading to the country. The plan is one night Matamata (for the Hobbiton tour), two in Lake Taupo, then heading back to either Rotorua or Tauranga, then back to Auckland. We’re used to driving - we’re Midwesterners. 
Hey, any recommendations for Sydney are still fine! Nothing’s set in stone other than the Bridge Climb and our accommodations (can’t remember where, my sister booked it).
We’re not leaving until the 27th so no problem, but thanks!
I’ll second this. I actually stayed in Manly while on a business trip to Sydney once, and really enjoyed it. The beach was beautiful, there was a nice walking trail through a seaside park, and there were any number of places to stop for a beer or some sort of coffee. The Corso was interesting to wander along and look in the shops, and there were often quite good buskers performing. And the ferry ride between Circular Quay and Manly is fun, too.
Rotorua suggestions:
Top 2:
Waimangu Vally (#1 personal favourite) - scenic walk down through very active, very recent geothermal area. Less touristy than most of the other geothermal attractions. Can combine with boat tour across Lake Rotomahana.(Waimangu valley website)
Mt Tawarewa - 4WD trip up volcano, scree slope down into crater, trek through crater, climb out. (General info from AA website).
After that:
Skyline / Luge – cable cars and unpowered go-karts. (Skyline Skyrides)
DUKW tour of the Rotorua lakes – silly but was a lot of fun. (Duck Tours)
Rainbow Springs - especially if you like fish and birds. 
(Website)
If you haven’t had a look at the Rotorua tourism site for “experiences” it’s pretty good, and most can be arranged / booked through the big information center (the i-Site)
And there’s a pretty good range depending on what you’d enjoy – my wife wouldn’t go for the jet boating or white-water (or black-water) rafting when we holidayed there in January, so I can’t comment on those.
Hope you have fun!
Skip one of the days at Taupo and go to Waitomo.
It’s a tourist trap, but it’s a worthwhile tourist trap.
Additions for Auckland…
If you want a scenic view you could try the top of the Skytower… if you’re more adventurous you can wander around the outside… or go the whole hog and jump off it. :eek:
Continuing in the “walking up volcanoes” theme you might consider a ferry across to Rangitoto Island. (Ferry times).
Or a tour of Waiheke Island’s vineyards?
On the less strenuous end of things… Auckland War Memorial Museum? If you want to have a look at things Maori / Colonial / Kiwiana.
Loved the east coast of the Coromandel Peninsula, an hour east of Auckland. Whangamata - great beach (at a town). Opoutere – even greater isolated beach.
In Sydney, find some time to really walk around the Rocks. See where they had houses that were literally dug into the solid rocks there. Think a minute about what it was like, starving, transported, never to see friends or family again, mostly.
I like to do that occasionally.
Of course, I also like to do historical walking tours, because I’m a giant nerd.
If you like museums that are different, then try the Crime and Justice museum, which I think still has the Underbelly exhibt going, and Hyde Park Barracks.
Mostly, have fun. It’s a great city I’ve adopted and I’m in love with it.