In some states, well Oregon at least, you are not required to have a windshield. All you have to have is the wipers!
Take that out as well as the rear glass and you have increased your airflow substantially and reduced your frontal area by a third or more!
I can see it now as the newest trend on here: Detachable front and rear glass. Imagine it, Metros topping 100 mpg.
Seriously, you know you want to try it.