Just a quick note if anybody else was having this problem, since it took me a while to figure out.
Problem: on my network regular admins could not see the Plugins page to enable available plugins. However, in the Super Admin > Network Settings > Menu Settings > Enable administration menus the Plugins checkbox was checked.
Solution: deactivate Pro Sites, then check the Super Admin > Network Settings > Menu Settings > Enable administration menus > Plugins checkbox, then activate Pro Sites.
I think Pro Sites automatically checks it, but there seems to be a bug. Anyway, this is an easy solution.
Thanks for the great plugins guys!