Certainly it's not impossible that it can happen that a Bronze member gets an upgrade out of the blue - but I wouldn't pin my hopes on it, that's all. As a Gold FF I've only ever been operationally upgraded once ever, though coincidentally on the BNE-SIN leg. As a Bronze and Silver, never even got a sniff of an upgrade without shelling out the points.

In regards to where to send the previous boarding passes, you can fax them to 1300 305 747 or mail them to GPO Box 4357 Melbourne VIC 3001 - if they were Qantas flights I've found they post the points pretty swiftly. Wish you luck with it all!