That's interesting, but I'm not sure it's wise. Here's how I do it differently. I only take on subjects that I know well, and I charge a lot for those subjects because I know them well and can post intelligently about them. If it's a topic that I don't know well, I'll usually charge less and post mainly questions on the forum rather than answers. Furthermore, just because a topic is interesting is no reason not to charge a good amount for posting on it.
I deviate on how much I charge depending on the content.. If it's something I know really well then I'll charge only a dime or two, because I don't need to do any research. However, when it gets to something hazy for me, I'll charge more. I'll charge up to maybe 40 cents if the posts take a bit of research, because obviously I'll want to sound educated. Essentially, it all depends on what kind of posting I'm doing... More interesting to me = cheaper, because I'm getting more benefits than just money. I'm getting knowledge