This is a Catch-22 situation. MyMoodle is a way of NOT letting student-level users access (or even see) courses they are not enrolled in (pardon my dangling prepositions). So if you enable MyMoodle you effectively disable self-enrolment into courses, as they are invisible to non-enrolled students.
You can probably play with the Front Page settings to make ALL courses visible to ALL visitors (including non-logged in) - but this defeats the whole idea of MyMoodle as a way of hiding and showing courses on the "need-to-know" basis, so to speak.
If you figure it out please post your findings here - it's an interesting riddle.