I figured out how to all-purpose-ify the image drag command.  Now with one command, it can handle multiple situations.  If you drag it:

Outside a selector/property (source.css): nothing happens
After a property (meta.property-value.css): inserts url('path/image.jpg')
Inside of empty parentheses in a property value: inserts 'path/image.jpg'
Inside of single quotes in a property value: inserts path/image.jpg
Inside a property list, outside a value: inserts a full background: shortcut tag.

Suggestions welcome.