Regarding the lip I would pursue the idea if I were in your shoes seeing as the car does see some serious track time. The underbody spoiler design you've got going will seriously help to reduce underbody flow and improve downforce. If nothing else make it a track only item if you are unsure of the looks (which I rather enjoy by the way). The car is so functional as it sits, the lip would be the perfect addition IMHO. We can all agree that the Corvette does quite well aerodynamically, so here is an inspiration picture for you.