If you're in Y, you won't a lounge anyway - unless you book the QF codeshare I suppose. But then, on the QF codeshare you wouldn't get the emailed upgrade offers.

You'll only have a chance of an op-up if you book a flex plus ticket (maybe a slight chance with flex). Even then, Platinum status will trump you, and any status in the same flex plus / flex fare band.

In short, I think it's a bad idea to throw away $360 on the off chance you may get an op-up. Then again, the A380 is much more pleasant in Y than QR B787/A350 Y.