Aerodynamics

That's pretty much exactly right, except that that a diffuser depends on a consistent rather than necessarily minimal ride height for its effect.

Further thoughts on the Esprit GT1 splitter (note that I'm reasoning from other types that I have seen the splitter/front undertray area on, not from observation of the type in question). I suspect that it may be a combination of a splitter lowering the front stagnation point from the bumper edge so about the splitter height, and a flat undertray back to the front edges of the front arches, with diffuser elements feeding into the wheelarches (and feeding brake ducts).