You don't list any info in your profile. If you do not have elite status, the number of miles you can earn is capped at about 60k per year.

It's true that on AA, 1 million lifetime earned miles will give you gold status for life. That said, I don't think this is anywhere close to worth it unless you have some pressing need for the 500k miles. If you have an Amex SPG card, that would be closer to worth it as 500k Starwood points are much better than 500k AA miles (including the fact that you could xfer the 500k Starwood points into AA and get 625k AA miles).

Also see this large ongoing thread on tax payments for miles here:
http://www.flyertalk.com/forum/showthread.php?t=527045