[spacemanspif]

Cant hurt to test the difference between a belly pan and air dam. When you go belly pan, you will still want to use tire spats to block the air hitting the tires. Harder core still would be tire boat tails front and rear (look up Arcosine's Saturn project for what I'm poorly describing).

I think OEM is using recessed air dams for multiple reasons. It's more hidden so it doesn't affect the looks of the car as much. Closer to the tires means you can go lower without scraping and it is less likely to get stuck on parking blocks. Also, some cars are set up as "bottom breathers" where the dam is actually integral to the cooling systems (C5 Corvette) and needs to be placed directly under the radiator.