Looking at flying to Europe next year with wife. Between us we have 320K points, earned through limited flights but more from card usage and bonus points. We are both bronze category freq flyers so I suspect have little chance of upgrades regardless of points. Am I correct, and if so would using points and pay provide better certainty of securing the seats? Does this cost more points?
Points plus pay will certainly give you a better chance of securing premium seats, as you have this option on every QF operated flight. However with your points balance I would suggest this is a massive waste of money, as points plus pay massively devalues your points compared to classic awards. The classic award seats are the only one I would consider buying; if it came to points plus pay, I would save my points and pay a cash fare.
Upgrading with points, either from premium to business or from economy to premium, is certainly possible as a bronze. Qantas will prioritise those requesting an upgrade who have higher status though, so you will be outranked by pretty much everyone on that score. After status Qantas consider paid qantas club membership as a boost to your chances, and then after that they will consider who is upgrading from the higher booking class.
I would suggest that if you are planning to travel in peak season or around school holidays your chances are slim, but if you were hoping to travel in say October/November or March I give you a good chance of getting the upgrade.
Best of luck!