The question of surface quality is not easy to understand. I will try to make a short explaination:
Between fluid and surface of the foil is always friction. This friction causes the fluid close to the surface (the boundary layer) to be slowed down. If the slowing down is to strong the boundary layer changes from a laminar state to a turbulent state. In general laminar flow has less friction drag than turbulent flow. The surface roughness is a major factor of this slowing down, but if the shape of the foil is not designed to have laminar flow, you will never achieve laminarity even with super smooth surfaces.
Conclusion one: If you have laminar foils, surface roughness is very important.

However laminar flow is very sensitive for early seperation (stall). That means that a non laminar foil produces in general more lift than a laminar foil of the same size. If stalling is a problem (manoeuvring) , rough surfaces may be helpful, especially if it fixes the transition from laminar to turbulent boundray layer close to the foils nose.
Conclusion two: Laminar foils are not always useful.

Shark skin or riblets are not only rough surfaces, but rough and ordered surfaces, which may reduce the friction drag of a turbulent boubndray layer by about 5%, without having the problem of early stall. This is a not pure theory, but also tested in real life on aircraft and boats. However this technology is not for free, I think 3M once produced riblet films, but I don't know about costs and stability of the glue.
Conclusion three: Shark skin is more than just rough surface

Hope that clarifies a bit the situation.

Cheers,

Klaus