If the brisbane route doesnt get you home any quicker then I would go via SIN, F/J all the way and lounges, no swaping from international to domestic. A long stop in singapore you could go into town, or watch a movie at the cinema in the airport and then hangout in the lounge/s
Thanks mooingchicken, and thank you to all the members of the AFF community who so readily offered advice, insights and alternatives. I really hope I can return the favour some time soon. The Brisbane seats have now gone, so that kind of made the decision for me, but I agree that not having to swap from international to domestic in Brisbane (and everything that goes with it) is the best option. And let's face it, if you are going to be in an airport for 7 hours - there's a lot worse than Singapore.
Thanks again to everyone for your very kind assistance.