Let's make a few assumptions to illustrate the point.
-You can get an interest rate of 1% elsewhere on a checking account. (Is this too generous?)
-You have a combined marginal rate of 35%. (Obviously this can vary wildly between people)
-You value AA miles at 1.6 cpm. (Which really depends on what you do with your AA miles)
At $200,000 (the account max) you would earn 240K AA miles or $2,000 interest pre-tax which becomes $1,300 after tax. 240K AA miles is worth $3,840 at 1.6cpm. The advantage of the BD account in this case is $3,840-$1,300-$144=$2,396.
At $50,000 you would earn 60K AA miles or $500 interest pre-tax which becomes $325 after tax. 60K AA miles is worth $960 at 1.6cpm. The advantage of the BD account in this case is $960-$325-$144=$491.
At $25,000 you would earn 30K AA miles or $250 interest pre-tax which becomes $162.50 after tax. 30K AA miles is worth $480 at 1.6cpm. The advantage of the BD account in this case is $480-$162.50-$144=$173.50.
At $15,000 you would earn 18K AA miles or $150 interest pre-tax which becomes $97.50 after tax. 18K AA miles is worth $288 at 1.6cpm. The advantage of the BD account in this case is $288-$97.50-$144=$46.50
At $12,000 you would earn 14,400 AA miles or $120 interest pre-tax which becomes $78 after tax. 14,400 AA miles is worth $230.40 at 1.6cpm. The advantage of the BD account in this case is $230.40-$78-$144=$8.40
Go ahead and plug your own numbers in to see if the account i still worthwhile for you.