I run two wordpress mu installs. They are both indentical in terms of plugins, themes and network-wide settings. The reason I run two is because they have different root-domains and different superadmins. Is it possible to simplify this setup somehow?
To a certain extent, yes.
Take a look at the WP Multi Network plugin. It allows you to have multiple, separate MU networks running off the same installation - same core, same plugins, same themes, same database.
Ron and @andrea-r are heavily involved in the WP multisite community.
They have a decent guide and an up-dated plugin with ebook at http://wpebooks.com/networks/
the plugin addresses the concept of a network of networks
hope that helps? Damien