Having a sagging headliner gave me the options of getting it redone either by myself or a shop, or to do a more permanent fix. I decided then to remove the headliner,  remove the fabric, scrape off the old glue and spray paint it with a flat black. I am very happy with the results. Here are a few pics of the finished process I did back in June 2009 and still looks good!  I don't believe the thin layer of fabric that I removed functions as an insulator.