How does one get Sitenotes to be editable amongst Admins? It seems like only Superuser can actually add a note. We would like for folks on the Admin level to leave notes amongst themselves. Is there a line I need to edit in the .ini files?

There's currently no setting to control what user roles can edit Sitenotes -- you're right that by default this is super users, and that's hardcoded into the plugin.

If you dig into the code of the sitenotes plugin, edit the index.php file locating within /admin/sitenotes/. On line six, edit the current code <?php if(has_permission('super')): ?> to grant permission for admin users, replacing it with <?php if(has_permission('super') || has_permission('admin')): ?>. This is just a fix for how it currently works, but you should be all set.

A future version of the plugin should actually use the ACL to control user permissions, but this first release was meant to be a simple solution. Let me know if this works out for you.