I think that for those who, like Dimi, use their cars frequently on the road, a roll down window isn't vital but would be extremely useful and pleasant. However, it would reduce the storage space available in the door.
Some years ago, before Ford put out the new GT, I studied this and proposed to a local kit builder that with a fixed front "quarter" window, a roll-down could be fitted if the glass wasn't really flush, but the back corner was inset slightly so that the glass rolled down into the door inside the latch mechanism and air channel recess. This inset could be disguised with a blackout or trim. The builder said the angles were all wrong and it couldn't be done, but I thought it possible. Obviously, the glass would need to be curved in one plane, and wouldn't roll all the way down, but I thought it would feel much better and be useful. Then what happens, but Ford follow this approach (successfully) with the new GT. If someone developed a kit for the replicas that could be retro-fitted into the doors, I think it would be purchased and fitted to many of the road cars, but it wouldn't be cheap.
In the meantime, the DRB road cars here are tending to use the Mk III type hinge out windows, with a fixed front quarter, plus lift off type hinges so you can have fully open areas that are quickly "windowed" again if locking up somewhere, or if it rains.
