Talking about aerodynamics without wind tunnel testing is the same as talking about horsepower and never going near a dyno.
Some good reading.
Click
Click
Reading that and then going there are the only ways you'll know if anything you do is worth it. Otherwise you could be making things worse than they already are. And lets face it, is a Type4 powered Beetle ever going to handle or have a top speed warranting any sort of aerodynamic change?