If you have leftovers, why not make up a test sandwich and see how quilting over the rickrack goes. In addition to your straight stitch, check out the decorative stitches on your machine. For example, you might want to try a feather stitch through the rickrack.
I don't think there is any right way or wrong way to do this; only what you like best. Also, I think it highly unlikely anyone but you would notice the "oddness" of the back if you do not stitch through the rickrack. It's amazing what others don't see!