Just a couple ideas from some Usenet newsreaders I've used:
- A "killfile" option in preferences to ignore posts by certain users.
- A "next new" button along with the current "next". This would allow you to move through the board w/o coming across messages you've already read without jumping back and forth between the messages listing page. It sounds like this type of option might be possible with the new way you plan on storing read/unread messages.