Perrepilot,
I gather you're flying a modern glass sailplane, On a K-21 or a K-23, you really notice the difference. On a K-8, Blanik, or T-21, it's not really an issue. 99 per cent of light aeroplanes are in the second category. Only on a modern design, composite structure, powered aeroplane does a wet or slightly dirty (fly-spattered) wing make a serious difference. On a mushroom-riveted Yak, PA-28, etc, you can see why simply by looking at it. On a Lon-Eze, or a Lancair, it may well make a difference, but these are few and far between.