Do you dive? Some wonderful diving in NZ, and well worth travelling around a few sites for a week.
Otherwise... well, it's summer down there so not sure what Queenstown/Wanaka will be like as when I was there it was all about the skiiing/snowboarding.
Also, Milford Sound is one of the most amazing places of natural beauty you could ever see. The two big glaciers on the south island (Fox and Franz Josef) are pretty spectacular.
Or just bum around in Melbourne for a week, drinking, hanging out, seeing cultural stuff, trip to Wilsons Prom, could even pop over to Tassie for a couple of days (Hobart's a quaint little city with a really nice harbour, and there are some stunning national parks on the island), etc. Melbourne's a city with a very cool vibe and much more relaxed and fun than Sydney. Sydney has the harbour and the beaches, but Melbourne is just cooler.
Edit: okay, just seen the dates again. So not summer, but still not ski season.
Also noted you're already going to the glaciers in your second post... I did love NZ, but apart from Auckland and diving I preferred the south island to the north, and you're already seeing a fair bit of that.
So I'd recommend Melbourne - Wilsons Prom - Tassie - Melbourne (I love Melbourne!)
Oh include Phillip Island in a Victoria/Tassie & environs trip too - fairy penguins! (Not so many at that time of year, but you can still see them)
Yeah, definitely plenty to keep you occupied using Melbourne as a base, and some of my favourite bits of Aus are included in that little itinerary.