are you a frequent flyer?
Maybe they will bump you up with your frequent flyer points. I suggest you pray to the Qantas Gods that your seat is double-booked and they bump you up. It happened to me and it was woooonderful. Mind you, they now have individual tvs now, so that takes some of the shine off B/C. If you can afford it, do it. I have made the US - AUS flight way too many times in coach.