Not sure how well the carbon fibre GTR bonnet will do in a crash, but it definitely helps in terms of cooling. For instance, the supercharger I have sits right under the vent on the passenger side. I mean, literally right under it. Superchargers get hot, so this is a great way of expelling some of that cool air.
You can often see the heat wave from the engine coming out of the vents when sitting in traffic. Pretty cool.
But the main goal is for the car to stand out and look different and aggressive.