Module that allows visitors to suggest modifications on a node
Apart from the notifications, Workbench along with Workbench Moderation seems to meet most requirements.

Drupal only has two states for nodes: unpublished and published. With Workbench Moderation, you can define your own custom states, e.g. pending, accepted, not accepted, spam.
You can then authorize anonymous users to edit nodes (make suggestions). These edits will create new revisions which will NOT be published until authorized users actually publish the changes.

Workbench Moderation also works well with Diff which allows you to compare different revisions to see the actual changes per field.

Finally, following nodes and notifications can be realized with the Flag and the Rules module.