Thanks to all.

I think that I'll stick to the original routing. Changing the intra-US segments doesn't really help with the mileage because of the crazy QFF earning scheme. (I fail to see how flying from ORD-LAS should generate less SC than flying trans-con, but there you go!) I'll try to email Qantas with the query about what I will earn on 3 class LAX-MIA and see what (if anything) they say.

Hopefully it will all work out in the end. I plan on booking this weekend via the AA RTW desk. Reading the forums it seems the safest bet.