In order to keep the barrier to entry really low, here is what I think could be done,
Show edit question or answer option to everyone including anonymous users (with captcha). If the user has enough reputation, allow the edit to be saved directly. If the user doesn't have enough points or if it is a anonymous edit, highlight it to the moderators + admins + anyone with edit access and they can review the edit and approve it. This could be toggled on/off in preferences in the admin interface. What do you think about this?