As always, booking when seats are released (around 330 days on AA.com) provides the best opportunity to obtain award seats.
The cost is something that each of us need to consider. The current AA miles sale can provide 270,000 miles for $US4786.88 ($US4425.00 + $US331.88 tax + $US30.00 fee).
One J seat SYD-LAX, one way, is 80,000 miles (MileSAAver). So that works out at about $US1418 (based on buying the full 150,000 miles, plus bonus), unless my maths is out. If I wanted to book 2 x J seats SYD-LAX on AA72 on Friday 27/10/17 (for example), they're available, as is the following day. Availability is always limited, but if you can commit to planning 11 months out, then that's best.
Of course, the AA miles may be used for award seats on other airlines, but finding seat availability is always the issue.
As others have said, we all value airline miles differently. The biggest issue for me is availability/flexibility.