The majority of race cars use marine ply for their splitters because as you would imagine it's water proof, Absolutely useless on the road, so unless you've exhausted the cars performance on track, then adding aero should be last on the list, as should adding power but let's not get started with that one. Another thing, for your aero parts to be effective they need to be low to the ground, really low to the ground, again making them useless for the road. That's a friend of mine, the aero is proven to work, he's added splitter, entire flat floor, diffuser, rear wing, etc.