And Now for All the Caveats
Obviously, some interesting work goes on in think tanks. And obviously some donors support that work. But there's a reason that the largest, most financially successful, most often quoted organizations--including the ones Dan Drezner focused on--are notable for their small ratio of original thinking, or even scholarship-based popularization, to recycled soundbites. That's what funders and the media reward. That's what makes a think tank a winner.
What's really sad is that the system obscures the interesting work that does go on in think tanks, including the high-profile ones. Good work suffers from the think tank stigma, which then leads good people to leave think tanks or not to go to them in the first place, which leads to a higher proportion of bad work, and so on.