"I have been lurking on a few boards and wonder if it makes sense to go for the AA platinum challnge with the idea that on a DONE4 I would earn enough miles to be/or be very close to AA ExP and earn 8 VIPOW upgrades on AA and still maintain Emerald status. "

It could be worth it. whether the VIP03s would be of much use to you being based in Australia is one question that springs to mind since they can only be used on AA flights. The price of award travel on AA can be cheaper than on QF; e.g. 1st Class Australia-Europe return on QF using AA miles is 160k miles whereas it is 270k miles using QF miles. J is 130k vs 220k. Also economy travel within and between Australia and NZ is only 20k in Y and 35k in J. 20k will only get you something like MEL-SYD in Y return using QF miles.

"The cost would be losing status from WP to SG on QF for 1 year as I would not be able to earn enough QF SCs."

You would still have OW Emerald which should help

Of course a drawback is that you would be back to only a 50% bonus mileage accrual when you drop to SG with the QF scheme.

Dave