As a general rule buying cheapies online via the 3 carriers websites is the way to go these days. Beats a airpass hands down. (The only time QF's Boomerang pass comes into it's own is if there are trans-tasman segments and by having no change fees etc.)

Having said all that, however, you have hit the absolute peakest of peak travel periods down here. The whole country seems to pack up and move from 26 Dec for 5 weeks. It's the summer school vacation period and between your dates mentioned, a lot of industry is also closed down as well. As a result, the cheapies may well be gone, or the fares on offer may be a lot higher than what one would normally find.

Maybe a quick research surf on segments you are looking at, adding up the $ value of those segments combined and comparing against a pass would be not such a futile exercise at this time.

Cheers.