I've been to NZ a couple of times; lived there for 6 months (and travelled round before coming home) and spent a month there the second time. So I'm no expert, but I know what I like! Here are my comments...
Auckland - worth a visit to see the sky tower and hire a car (or find a bus) but I wouldn't stay too long - a couple of days or so would be more than enough.
Waitomo - Good idea. I skipped Waitomo and went to some glow worm caves in the south isle instead, but they were rubbish, a real disappointment..
Rotorua - Yup, spend a couple of days here at least, make sure you see Wai-O-Tapu...
Taupo - Another good stop. Checks out Craters of The Moon for some free thermal action!
Wellington - Lovely city, could easily spend a few days there. The museum is fantastic.
If you can, I'd also go and see Napier; a lovely art deco town with a stony beach and zero nightlife (!!) It's really quaint and pretty though...
Abeltasman - Yup, good spot for Kayaking.
Barry Town - Never heard of it! While you're on the West coast, avoid Westport and Greymouth unless you need a bed for the night! They're really just 'passing through' places...
Frans Josef - Yup, full day glacier hike is awesome
Wanaka - Nice, quiet place. Very pretty.
QT - I did a helicopter ride here, it was fantastic!
Kaikora - Stop here for a whale watch or dophin trip but I wouldn't spend a massive amount of time...
CC - Another lovely city, feels quite English
Have you got time for a stop in Lake Tekapo? There isn't a massive amount there, but there are some striking pale blue lakes (glacier water) that make for good photos.
Also - I think you might be missing one of the highlights of NZ, Milford Sound, absolutely stunning scenery, mountains and waterfalls... 
Hope that helps - give me a shout if you want any more detail 