For those of you who have the moon roof deflector and/or side window visors - Why do you have them? Do they have any real purpose?

As far as I know the moon roof deflector was never made available and will not be. Shame, we put one on the wife's Jetta, it really helps with wind noise.

Moon Roof Deflector - Keeps your car from being hit by moon roofs.

I put the side window deflectors on my last truck. The main use I had for them was to allow the windows to be slightly open if the day starts sunny and it not rain in if it rains later.

do those window deflectors reduce wind noise significantly?

I can't recall one way or the other. They've been on the truck for the better part of ten years. While going down the road, it was usually windows all the way up or all the way down.