Hi Greg, I would argue that you don't necessarily need the reference back to the drawing file, if you are embedding properties such as Part/Drawing Number, Description etc from the drawing data card to the PDF data card. You could always create a search favorite that finds PDF files only, and type in the property(s) that is common to both files
I definitely agree with your statement.
Within our system currently, a PDF joins the workflow and follows it through to get reviewed, released and distributed just like any other design artifact. Without the reference, the PDF wouldn't show up in the reference tree upon transition and therefore get left behind. I guess I could always not have the reference and have users selectively push the PDFs/DXFs through the system. As you say, they have all the embedded information they require.