Very impressive followup. I've skimmed that.
My less meticulous conclusion is that melatonin makes me wake earlier and easier with light (maybe in general, but I don't wake by alarm). I haven't bothered to check whether that means I actually slept better (in terms of improving my performance/mood going forward), but I consider it a good sign.
So you are still using it?
Full essay: http://www.gwern.net/Melatonin