Hi, can I ask, what is wrong with using the 'guest' role for the 'default role for users in a course'?
I am also trying to work out how this all works, but it seems that if you set 'default role for users in a course' to guest then this avoids users getting added to the participants list and the courses visited as a guest showing up on the 'My Courses' list, but still allows the casual visitor to view the course.
Then (depending on your policy) individual course 'owners' can set whether they want to allow guest on their course or not.
Martin