Thomas, like I said, I use WP All Import all the time. The “Update existing posts” option has a setting near the end of the import setup to create new post for new records. So the update becomes and update or insert. WP all import also has hooks at all of the important places in the process so that you can even filter what it’s doing http://www.wpallimport.com/documentation/advanced/action-reference/.
I agree that it’s still impossible to rule out user error though, simple things like “XYZ” not being equal to “xyz” just go right over the head of most of my clients.
