Did you try the Advanced Mindmap? I haven't tried any of them but from that plugin's write up:
"This Advance Mindmap module allows you to create mindmapping activity in moodle. Added features include: - Every user now have a separate mindmap in one single activity..."
No idea if you can grade them though.
I will go back and take a look at that. I did not do the advanced module, no. I will check it now. Thanks!
Good to hear you're getting closer to a solution. Re grading, again, something I haven't used but you could always set up a manual grade item.
Not the best workflow but as far as I know the only workaround at this time for what you are looking to do.