QF is pretty good at yield management , so involuntary upgrades are rare beasties. In the rare cases that they do occur, then having QF Platinum status is more likely to make you chosen, however there is nothing published as a benefit regarding it and they may move anyone as they please
If you book a business class seat with Qantas, expect to travel business class
As far as the details of the thread you refer goes, if interested in spending miles, I would be recommending AA , however he will only attain Platinum status (OW Sapphire ) whilst QF will get a higher status of Platinum (OW Emerald ) but will have poor redemption rates; Pretty card or better redemptions is the call to make
Dave