Could you comment on what I wrote before...
> What would happen if I edited the student role to be available at category level, and then assigned
> all the relevant users to the role of 'student' (from the category management page)?
> Would that be akin to enrolling them in all the courses in that category, without actually enrolling them?
That is pretty much what category enrolments. With the official Category enrolments they are enrolled in the courses and can post to forums etc. Each time a new course is made they will be automatically enrolled in that (should you wish)
Although category enrolments has a warning, I have to say I haven't personally seen many people complaining about performance issues with it on here - so either it IS ok, or those people don't come here to complain (or nobody uses it, but as it was such a popular feature in earlier versions of Moodle, I think there will still be people around using it.)