Replace button that looks like a "plus" (that links to node create form) with a button that looks like "new document"

My clients seem to have some trouble with the buttons for noderelationships actions on nodereference fields.

Consider:

I think this interface would be improved by simply changing the "plus" button to a "new document" button, for example:

This icon removes the confusion between adding a value to the cck field, and adding a new drupal node.

I'm not suggesting that this specific icon be used in place of the existing plus icon. It's just an example.
Thanks for your consideration.