There is a heavily modified Jetta in my neighborhood that has a carbon fiber hood. I’ve been trying to find it for a few days now but I guess the owner must be out of town. Here’s a picture of a Golf IV with a carbon fiber hood. While carbon fiber is used extensively in sports and exotic cars to reduce weight, tests have shown that there is a certain expertise required to execute this so that the use of carbon fiber will reduce the weight of the car.
Of course this is all relative. Can a Jetta with a lighter hood out run a Jetta with a factory standard hood? Perhaps. Over what distance? Aesthetically, it may not to be my design taste, but to my “boy-racer” taste… maybe it looks cool.