Induced drag decreases with airspeed, form and parasitic drag increase with airspeed.
The coating is probably so far aft on the wing and close to the fuselsausage that its effect is negligible. Sometimes a rough surface downstream of the transition from laminar flow can be beneficial by energizing the boundary layer from the free stream (similar function to vortillons).
Sharks have been imparted with this gift of textured skin too. On them, their skin has small ridges (like couderoy). 3M was working on a skin surface for Airbus a while back that had similar textures. Last I heard, they were experimenting with different ridge spacing and heights, but it was really expensive stuff ... like a hundred bucks a square foot. An A320's wing area is around 1300 ft², so it better offer big savings.
The ridges are called "riblets" is they're prependicular to the flow, "rivulets" if they're parallel, and they both make a swhooshing sound as the airplane taxis around the airport.
Up next, "speed holes"...