FWIW, I have had good luck getting better seat assignments on VA-operated flights, short and long haul, by inquiring at checkin or the lounge. I've found a VA domestic lounge is the absolute best place to ask - the agents in there are fabulous. Don't expect a class upgrade (although it's happened, particularly on leisure routes like NAN-SYD), but at least a decent aisle or bulkhead seat should be possible if they aren't all assigned on day of departure.