Hi,
As far as I know for upgrading My Inbox to 2.0 will require you to just upgrade the UIX01CA1 component from release 100 to 200. Other apps that you mention - Approve Shopping Carts, Approve Leave Requests have other UI components, they have nothing to do with the UIX01CA1 component. So upgrading to My Inbox 2.0 should not have any impact at least on these apps.
Regards,
Saurabh