[aerohead]

I like very much what you've done and I certainly don't want to discourage your efforts,but I wanted to point out that Nissan has done enough under car aerodynamic refinement on the Infiniti that they've published advertisements showing only the underside of the car.
Bottom line ( no pun ) is that you may not see gains,as say,you'd see on a Jeep,Land Cruiser,Rover,Tahoe,Suburban,etc..

Your refinements will put you in good stead for tail modifications should you choose to pursue that in the future.Nice work!