Given the choice between these three wing designs...The smooth one seems most popular even with airlines. For sure barnacles on wings would not be great on fuel economy, as the drag from the growth decreases lift. Airlines will clean the planes regularly since even dust and dirt increases drag.
If dimples were awesome I think we would see more of them since they can't be too hard to place. When I go to fly I see dull aluminum surfaces. Not even as polished as my rudder.
The centerboard on my 170 was beat up pretty bad when I picked it up. When up, the centerboard still protrudes about 1/2 inch below the hull. When grounded/beached the entire leading edge is exposed and gets chewed up. The centerboard gel coat was also poxed pretty bad. Finally, it is very hard to clean the centerboard since when on the trailer it can't be lowered. It was black with growth in the centerboard casing.
After resurfacing the centerboard, I noticed a significant improvement in pointing and better speed. The centerboard was re-gelled, then finished with wet sanding to 1400 grit and then polished with an electric buffer. There is some orange peel, so...dimpled?