I would bet that you are correct ... the springs are not making your headliner rattle and more work on the headliner will have to be done. Everyone else who posted here about the rattles in headliner getting fixed never mentioned the springs getting replaced. Since you don't feel any abnormal vibrations then the springs are probably fine.
Whatever they want to do to isolate the problem can't hurt though I guess. Goodluck and post back your results! Thanks ... I also had a few rattles in the headliner especially around the moonroof but fixed them myself for now.