My intention was to provide a site-level config if the plugin is activated at the plugin level, and a network-level config if the plugin is activated at the network level.
Generally, I think blog admins should be able to configure their own plugins if they have been given the right to administer everything else on a blog. However, if the plugin has been network activated, one would presume that there are a couple reasons:
1. the network admin wants to mandate image optimization, and would also probably want to mandate certain settings
2. the network admin wants to make things easier to manage and not activate the plugin 50 times(which I think is the case for those who have posted here), and so they would also like to configure the plugin once for all 50 blogs as well.
With that in mind, I think my plan should cover most use cases. And it shouldn't be too difficult to tweak if someone wants to activate it network wide and permit site admins to configure the plugin.