It's an interesting discussion going on here and for my 2 cents worth i find that personally i don't mind that QF staff deadheading are taking up so called valuable seats in J.
I could be slightly deranged, but as a fare paying passenger i find that there is one surefire way in order to guarantee your seat in J and that's to purchase one straight away, rather than trying to use points to upgrade from Y at a later date. At the end of the day QF have not made any guarantee that an upgrade can occur, but they have made a guaranteed that the next flight has crew.
I also understand in the world we have the tendency to be a focus on the self....as in i missed out on this or i missed out on that. But as a PAX on the sector that is being served by a crew member that has been required to deadhead into position, i want them to be as fresh, alert and attentive as possible - so if this means they take a seat up in J on your flight then

!
As for the catering, isn't it up to the operating crew to recognise a staff member in uniform (pretty easy as others have said) and say to them I'll come back to you when im finished serving the other passengers. Because last time i checked as a PAX (and im guessing that deadheading crew are the same), we don't get to see the amount of meals that are onboard.
For the record it's my first post and i dont dislike anyone