I'm a little confused on the original premise... how is I/D at LAX any worse than D/I at SYD? I've done MEL-LAX-xxx and haven't had any noticeable issues.
In re (1), I'm not super familiar with RTW fare construction, but I thought the whole ticket was covered by one (RTW) fare, and I don't see that it would not allow QF sectors intra-Australia. I don't think the MEL-SYD-IAH option would include an embedded surface sector.