I've just done some calculations.
In the last 3 years I have done 12 return trips to the US on QF - each of them to either LAX or SFO. I've always booked discount economy, and on some of them i've flown onward in the US on AA.
3 of the trips have been with my wife, and 9 were on my own.
We/I have never been upgraded when we have travelled together.
Of the 9 other return trips (18 flights), I have been upgraded on 11 of them.
I've been in Y+ 8 times and J 3 times, and I have only used points for 1 Y+ upgrade.
I have not long moved from bronze to silver and my first flight as a silver got me upgraded to Y+
I have asked several times how the upgrades work, and why I have got them and in almost every case, the FA/CSM has just smiled at me and said I'm lucky.
My most memorable upgrade was about 8 months ago on a LAX-SYD flight via AKL. When I checked in at LAX I was in Y and I asked if I could get a bulkhead seat. I was told she could not change it, but to ask at the lounge, which I did. The lady at the QF lounge smiled and said "you should be happy with this" and I was in J! But it got better --- there were only 2 of us in J for the whole flight to AKL, where 6 more joined us to SYD.
Economy on that flight was about 50% full, so my upgrade made absolutely no sense in terms of freeing up my seat to sell to someone else.
I'm not famous, nor am I a high flying executive - I just own my own small business in Adelaide. But my late dad did work for TAA a very long time ago in senior management, so I'm working on the fact that he is looking after me