Create "suggest an edit" functionality for anonymous users on nodes
I think you may want to check out the Workbench Moderation module. Basically, you'd configure a workflow that allows anonymous users to 'edit' a node, but their edits would trigger the workflow. From an admin experience perspective, you may want to configure it to trigger an email notice whenever updates have been made, or otherwise alert content admins that suggestions have been made.

One potential gotcha is the way that Workbench handles revisions -- it doesn't fork. Meaning that if you publish a node, that becomes revision 1. If someone comes along and edits it, they suggest revision 2. If a third person comes along, they'll see that the node is on revision 1, but when they go to edit the node, they'll see it's on revision 2. Any changes would be saved as revision 3, and so on. You may need to extend the module with your own custom workflow if you're looking for forking behavior (think pull requests on GitHub).