Interestingly, this article [0] states that the opposite is true: "The research included vintage cars up to 70 years old to see if their less aerodynamic shape meant they killed more bugs, but it found that modern cars actually hit slightly more insects."
That seems plausible. Perhaps an car with poor aerodynamics pushes a wall of air in front of it that deflects bugs up over the car, where a slippery car may allow the bugs to smash right into the glass.
Now that I've made my comment, I'll go read that article. Thanks for sharing ;-)