Could someone please explain the principle behind the plastic air dams on the underside of the TCH in front of the wheels. I believe contrary to what you would think they reduce drag. Does anyone know how significant they are and if there is a drag coefficient published for the TCH.

Drag is not always easy to predict or foresee, because it becomes very complex very quickly. For example a golf ball with small dimples on it's surface creates less drag than smooth surface ball, contrary to what one may think. if I had to speculate I would think small air dams redirect the airflow down and to the sides to disturb laminate airflow along underneath of the body going to the wheel well. In other words small turbulence created by the plastic pieces lowers the turbulence of air entering the wheel well and tire. Similar to small dimples on golf ball creating small air disturbances up front and lowering negative pressure in the back at the same time, with net result being lower drag total.
This page explains golf ball aerodynamics in very simple way:
http://www.fi.edu/wright/again/wings...r/golf-01.html

I think Wheel Spats are something different. The Ferrari Formula 1 team started running what they called wheel spats this year.
(see link)

I would guess that the little winglets are to reduce drag .... or could it be to help reduce road noise?