I found this great article on rejsa.nu covering aero modifications to racecars.
Splitters, wings, skirts and diffusers are explained with examples and illustrations.

http://rejsa.nu/info/aerodynamik.pdf

I didn't know that a splitter can aid cooling by increasing the pressure in the front of the car. It makes sense though as its main purpose is to restrict flow under the car by forcing air to go over the splitter.
My plan in the future is to make a ghetto plywood 2 piece front splitter that can be mounted at the track and small enough to fit into the car
I would need to have some kind of mounts at the cross member that it could slide into and 4 or more mounting points in the front. It would also need to be ~ 50mm off ground so a 3rd piece would be necessary to fill the gap between the stock MSM lip and splitter. Hmm...
Right now it is way down on the todo list an will probably not happen before next year, or worse. Or never.