Without a doubt "Mystifies Me" is one of my favorite things he's done and I thought the covers and reworked traditional stuff on the UT albums were great. I don't think doing covers is bad nor does it mean you can't write songs of your own that aren't equally great.
Jay doing other people's tunes. Some of the most exciting things I've heard him do were written by others. Not knocking his outstanding songwriting, mind you. But "Mystifies Me", "Shake Some Action", "Looking At The World...", et al kick ass. I'd love to hear that record.