Good question... I tried nutmeg once, it gave it a more traditional sweet potatoes taste. I also tried pumpkin pie spice, same result but a little more pizazz. ;) The way it is, kind of resembles pecan pie.
I'd bet pumpkin pie spice has nutmeg as well as cinnamon and a few others, but I dont know. They say that the best nutmeg is when you have the thing and grind it yourself.