I can understand your opinion...knowing what I know, and doing this sort of thing for nearly 20 years, and all of the texts and emails Rob and I exchange on a regular basis where we say we would feel comfortable posting what we have behind a paywall, but not on free boards for a variety of reasons, I disagree. But again, to each his or her own.
The paysite is probably a great idea, although I don't think I will be partaking (the opportunity-cost tied to the time I waste on this site is bad enough, I probably should not compound it by taking money out of my pocket). But I am curious about the idea that there is some information that you would feel comfortable sharing behind a paywall, but not otherwise. You said yourself that you hope that information will stay private, but you know that ultimately it probably won't. And when it comes out (e.g. on Twitter, your free site, a rival free site, etc.), it will still be attributed to you, which it seems to me could still result in burning your sources. So doesn't the end result end up being the same?
Feel free to answer or not; it is not a critique, simply genuine curiosity on my part why the paywall would make that much of a difference in this case.