Please consider the possibility of added a "By invitation" feature to a thread. The basic idea is that the thread starter will be able to identify the thread as "By invitation" (either for posting or for posting and viewing). The thread title will still show up forum and the moderators will still have full power over the thread

This can make some threads less problematic (e.g Miami four points) since people which didn't stay in the place could be kept from posting (by the starter); enable limiting participants of a poll to a defined group of users, allow sub-groups (e.g. Do, Mistake fare) to have a more private discussion without the "benefits" of views from non-participants, less impacted, users and removing the possibility of non-users having access to the information.

I believe that this will actually reduce the load on moderators since each such thread will have a limited power moderator (the starter) and will be less likely to get spammed or derailed since the starter get to control the participants.