Hey @jonnymiller
I was checking this out and I overlooked something in the 2.0 release. I have just updated the plugin (ver 2.1).
To answer your questions:
Does this plugin allow me to change admin theme css network wide, from the top level?
Yes. That’s the exact intention of the plugin.
When logged in as Admin there is no “appearance” menu item, the only way to get that is to go to an individual child site … I want to change something network wide, not allow each site to change it individually.
The Admin CSS MU menu will be in the Appearance Menu of the MAIN SITE (and only for a network Admin). i.e. if your Multisite network is on example.com, you will be able to see it at: example.com/wp-admin/themes.php?page=admin-css-mu
I hope that helps.