Thanks, I will contact Qantas and enquire, but I do think that if you are wanting to spend more money with them, they shouldn't charge you on top of that. I am wondering often if my loyalty to Qantas is worth it ??
It all depends on the original fare you have paid and the conditions of that fare. EVERY AIRLINE DOES THIS so your point about loyalty or not is a bit moot as you'd have the same issues on Cathay, Singapore, Emirates, American, Aeroflot etc.
This is the whole idea of fare structures - if you purchased a flexible economY ticket then your fare change fee would be probably zero, but if you purchased a deep discount fare, then the change fee is associated with that fare type (because it is so much cheaper) NOT that you are wanting to pay for a higher fare type (for example, many cheap fares have change fees for date changes, which is not an upgrade to the fare type)_
Having said that some high tier elite FF members can have some fees waived, but more often than not the change fees on cheap tickets are fairly binding for that reason - they're priced cheaply with those specific conditions as part of the pricing model.
I'm not meaning to have a go at you personally, but this is basically the model. Again, if you have purchased a more flexible fare type then change fees will be less, or even 0, to upgrade the fare - but this is why it's a flexible ticket as opposed to a deep discount or sale fare.
The best way to guarantee a seat in the cabin of your choice is to either pay for it up front with $$$ or points(if an award seat is available). The rest is a lottery based on the specific flight loads and demand and other passengers with upgrade requests that may be ahead in the queue based on fare type and/or status.
And a final note, you mention SYD-DXB as a flight - make sure it is not a QF codeshare on an Emirates flight (eg QF8xx_) which you would not be able to upgrade on with QFF points. So you'd be looking at QF1 and not something like QF843