People who track their cars often drill the grille (... forgive me) to open it up for that. The most likely function of it being partially blocked, from my super basic and limited understanding of aerodynamics, is to move air around the front of the car. I don't know if anyone has done before and after testing with it. Just be ready to paint your crash bar black if you choose to do it.
The engine bay cover is just to suppress the noise of the loud ass injectors. I'm not sure if it serves any other purpose, really.