Personally I could see going for a different Emerald if you could not achieve it on AA, but only for that reason. As an EXP it's only $250 for lounge access. Weigh that against your 100% mileage bonus (or the difference between that and whatever program, typically 50% top tier) and the value of the miles just blows $250 out of the water by itself. Add earn/burn rates to the equation and it's sweeter still.

I understand you want access to the Flagship lounge, but is it worth that much? If free drinks is the interest you could get a QF club membership instead of AC membership and I believe that problem is solved.