The valance panels typically provide three different purposes, which vary with teh vehicle application:
1 - Hide ugly suspension pieces-parts so the wife or non-automotice types don't get apoplectic when looking at the car on the dealer's lot (e.g. "honey, what is all that ugly mechanical stuff showing down there", kind of like all these fru-fru underhood engine covers so popular these days).
2 - Smooth the airflow going under the car for better gas mileage and improved high speed stability (true, but the one on the Ex would not seem to make much difference; however, look at the underbody on a true exotic car - smooth as a baby's bottom). This, in addition to option #3 below, is what the one on my C6 Corvette does.
3 - Direct flow to the radiator, or better said, to prevent air bypassing the radiator, sometimes by creating a high pressure area directly in front of the area just behind the grill. Again, I am doubting that the one of the Ex could possibly do much for this, but I an no aerodynamicist. This is what the one on my old Volvo brick actually does.
Can you take it off without impact on an Ex - I'd bet money on it.