There is a lot of evidence that smoke in battle did influence the outcome of gunnery, and that it was one of the factors which helped downwind ships as they were not impeded from seeing by their own gun-smoke. Depending on the wind direction and speed, smoke could be a real handicap to rapid and accurate firing. I think an optional well considered rule could not only add an extra dimension to the game but also induce Captain's to plot their approach to battle with care.
Rob.