My advice for the OP, is to have a set of alternate flights available both on Qantas, American Airlines, and other OneWorld partners that will get them to their destination on time. And then, if Qantas ends up cancelling your flight, or if you misconnect, you will have alternate flights to offer Qantas to get you there. Remember, if Qantas cancel your flight or if you misconnect, Qantas is obligated to provide you with suitable alternate flights at no additional cost to you. It does not matter if the flight is operated by Qantas or not. it does not matter if the only fares is available at the time for Qantas to rebook you on to are higher than what you originally booked, they just have to do it.
They don’t need travel insurance, since the Montreal convention on air transport 1999 clearly states that airlines which deliver you late to your final destination are liable for up to $7000 US in reimbursement related to things like activities booked during your travel.