How to enable Admins to see Plugins

Have a look at the Network Admin Settings screen (in my installation, it’s at example.com/wp-admin/network/settings.php). Tucked away down near the bottom is this:

Menu Settings

Enable administration menus [] Plugins

Checking that box should allow your users to see the Plugins menu in their sites’ back end. (I don’t think it’ll allow them to install new plugins. I haven’t tried it out yet, though, so test it before you put it into production.)