I wondered if using the trac system might make things easier for the staff to keep track of ideas, requests, and bugs. It's a ticket system built for this kind of thing, and it looks like it can integrate with phpBB to share the same login.
It'll make it easier to go through and accept/reject/close things, can keep track of priority, set an owner to handle it, and so on. It still allows discussion, and can take attachments too for logs and such. It looks like there's a way to make hidden bug reports for possibly exploitable bugs that shouldn't be public.
Drawbacks are it looks a little tricky to set up, and it may use more server resources (though probably less than the forums).