Not sure if there's a question in there, but I'll try and offer a few points:
1) I believe "not-for-profit" is the technical equivalent of "non-profit", so there's no great conspiracy there.
2. There's two schools of thought on the $500k vs $11 million comparison. The first is that that's a too-small % of dollars on advocacy. The second is that way too much of the National PTA's dollars go toward overhead (60+ employees at headquarters) and bureaucracy -- as opposed to helping local groups. But I don't think National is "sitting" on any dollars. In the last few years, National has actually been spending more than it takes in.
3. Finally, you're exactly right that individuals can join the PTA, even if their groups are not PTA. The link is here:
Recently our school's parent organization began visitng the PTO or PTA question. We are currently a PTO. While I did not read EVERY post on this subject, none of the ones I read qustioned the National PTA financial statement. The most current one I read online (2001) showed 11+ million dollars in assets and only 500+ thousand dollars spent on advocacy. It bothers me that the National PTA is a "not-for-profit" organization and not a "non-profit" organization. Why do they sit on all that money? I am just too naive? Does someone have an answer? Also, just because a school chooses not to be a PTA and commit that money toward national and state membership does not mean that any individual can not become a member. If one feels so strongly about the PTA's reach beyond the scope of one's school, join on one's own.