The "power elite," as described by Irving Kristol as those "shaping policy," ultimately need funding. Smartly, many of these "think-tanks" do not disclose their major sources of funding.

New America Foundation, probably in a bid to be open and transparent, does disclose its major funders.
http://www.newamerica.net/about/funding

Now, those major foundations, while they do ask for donations, are kept open and growing by their massive investment portfolios in sometimes in-house and in other times separate investment companies. I know because we manage a great deal of their money. And I mean MASSIVE.

I am sure a great deal of the time their civic or social purpose is admirable in the minds of the trustees, however their influence may aid in creating poor policy from the perspective of American society, that is if you believe in liberty.