1. I would pay my fair share for maintenance of the free site. I really have no idea what the site takes to run. Is it more than a couple thousand a year? Does any know the operating costs? I also think a "contributor" icon in one's profile would spur people to donate, whether out of obligation or shame.
2. I agree that a pay site would be detrimental to the free side. What if someone had "inside information" about a relevant topic that's being discussed on the pay board, but that person was not a premium member? If he/she posts that info on the free board, my understanding is that the person gets scolded for sharing the info with the peasants, even though he's not part of the aristocracy. Thus, info is stifled at the source.
3. What I would pay for, in addition to upkeep/maintenance, is a board that is well organized and moderated in terms of thread topics. I don't think it need to be as restrictive of other sites which essentially prevent creation of new threads, but there needs to be a better way to navigate through the morass of similarly-intended threads.