There is times when I feel the vent window is important. What I have noticed is with window down and the vent window open it blocks the air from hitting you. It also helps with defrosting the windscreen. I also like the touch of chrome it gives too. Just my two cents.
Would need some form of gasket along the windscreen frame for the glass to seal against. Is there room inside that door shell for a full piece of glass ? Wouldn't door hinge, door stay and other gear get in the way ??