Well a couple of weeks ago, I booked QF business class flights ADL-MEL-SIN return with the SIN to MEL leg code share on the afternoon EK B773 departure ex-SIN.
It was I class discounted business class fare but towards the end of the booking and ticketing process on the QF website, I was offered a paid upgrade to F on the EK operated SIN to MEL for an additional AUD 130.
Of course I snapped it up. This leg was booked into A class and the tag-on domestic MEL-ADL was booked into flex J class, so opportunities for earning even more SCs.
But for AUD 1000, I probably wouldn't.