Aside from air being a subset of liquids, one must consider several things before choosing the surface roughness.

 

A simplistic view of the Reynolds number for an airfoil is the air speed times the chord length divided by the viscosity of the air.  Thus, a glider at 1/4 the speed (50 vs 200 KIAS) and with a chord about 1/2 of a Lancair 320 reduces the Reynolds number almost an order of magnitude when trying to compare characteristics.

 

Laminar flow has been compared to tossing a deck of cards across a rug - each laminar strata sliding over the one beneath it.  Air to air friction is low (like card to card) until the bottom layer of air against wing (card against rug).  There is concern about the friction induced drag.

 

All things being equal, at high velocities skin friction drag increases.  At low Reynolds numbers, skin friction becomes less of a drag component than the transition from separation to turbulent and the subsequent wake - where viscosity has more of an effect than velocity. 

 

Certain bodies passing thru air more slowly can have the wake drag reduced by not allowing laminar flow to take place thus inducing turbulent flow about the body.  Golf balls and bicycle racers (dimpled helmets and rough surface suits) come to mind.  Maybe even slow moving gliders.

 

Anecdotal evidence that roughness is good for high-speed laminar flow would be to find a Reno racer that does not maintain a smooth surfaced wing and a very highly polished prop.  The prop is interesting since the outer third of the blade is probably operating above .7 Mach.  My prop tip is at .75 Mach (Sea Level, 15C, forward movement not counted),  I think I will polish and wax the sucker. 

 

I will happily race anyone that roughens up their Lancair 320 wing.  Hmmmmmm.... Maybe even a 360.

 

I will be even happier to race a 320 powered spam can - rivet heads being similar to the obverse of dimples.  Maybe even the leading edge paint will be spider-webbed from sitting out in the sun for twenty years.

 

No, not this Spam Can:

 

the other ones.

 

Finally, if you long-board sanded your wings enough to remove the waves, applied high-gloss paint with no stripes or fancy checker-boards tripping the airflow and use a product such as Dri-Wash (polymer coating) to further slick up the surface, you are ready to rock!