You make some good points, on some I agree, and on others I don't.
But I'm with you on one thing: give us back what we paid in, and shut the damn thing down.
We will never have any idea about the AARP membership numbers, because they give memberships away, often to people who don't ask or care. They won't release their numbers. Modern Maturity magazine has a stated circulation of 22,000,000. I don't know what the US population figures are, of people 50 and over.
And the boomers DIDN'T give you legalized abortion, the Supremes did.
Okay, the AARP claims 35 million members. From their site at:
http://www.aarp.org/leadership/Articles/a2003-01-13-aarphistory.html
US citizenship is not a requirement, over 40,000 are members who are citizens of other countries. Their budget is supposedly around 600 million a year. Main office is in DC, where else?
There are 77 million boomers, so you are likely close in your estimation that half are AARP members. I don't like that, but I also don't necessarily believe their figures. I'll have to do some more looking around...