Are you sure they charge extra? When we rented from them, they didn't charge any extra - that was one of their selling points! Well, maybe they've changed their policy since we were there....
Yes, I think the windshield is a necessity. You will be glad you have it when it gets chilly in the early mornings or late evenings. And, if it's raining you will definitely be glad you have it!
Yes, at FW they only have windshield golfcarts, and I don't like the windshield. It really seems to make it harder to see well at night, IMHO. Does anyone know if GCE has any WITHOUT the windshield?