From fact to fiction!
It is amazing how the details of a story can morph in folk lore from something that is probably true to something that is completely backwards!
Rutan well-understands the importance of smooth, wave-free contours on highly loaded canard airfoils.
If Burt ever sanded anyone's canard, it would have been with 600 grit, not 60 grit!
Canard airplanes (that are statically stable) ask a lot out of a canard. It is a very highly loaded lifting surface. To achieve the high lift values with good performance, airfoils are used which require good laminar flow on the forward portion, followed by good transition to turbulent boundary layer to survive the aggressive adverse pressure gradient on the rear portion of the airfoil.
The laminar portion must be smooth and free of waves. Sanding would be a must to remove any waviness. Even orange peel from unsanded paint may be enough to cause early transition, which will kill the lift and increase drag, both. Very fine sanding (at 45 degrees is good) will help with wetting out rain drops that can seriously degrade the lifting ability. Otherwise, after sanding to remove any waviness, polished would be best.
Canard lore is full of stories of rain causing serious problems, and especially a painted accent color stripe along the leading edge. The step along the masking line between colors would be a disaster, could even prevent a canard airplane from rotating for takeoff.
Now, you might reasonably say, "Hey, wait a minute, you keep telling us that a turbulent boundary layer can better survive adverse pressure gradients without separation (such as roughness on a ball) and yet you are telling us that early transition to turbulent boundary layer caused by bugs, rain, waviness, or lack of smoothness will kill the lift. This seems contradictory!"
And it does seem so. But here is the distinction. In order for a turbulent boundary layer to survive the very aggressive adverse pressure gradient on a thick, highly cambered airfoil (look up Liebeck airfoils), the turbulent boundary layer must be fresh, young, and healthy. Well energized. If you have premature transition because of bugs, rain, roughness on the forward portion of those airfoils, the turbulent boundary layer is pretty tired by the time it gets back to where the adverse gradient starts, and so, even though turbulent, it will separate. This results in significant lift loss (stall) well below the angle of attack where stall would normally occur on the same airfoil that is properly smooth. And of course, even at angles below that premature stall angle, there is also a significant increase in drag from the loss of laminar flow.
You might also point out that there are times when forcing transition from laminar to turbulent boundary layer is a good thing. We use zig-zag tape, or bumps, or blow-holes, or a variety of other tricks, to purposely cause transition just ahead of some place where a fresh, young turbulent boundary layer is needed to reduce/prevent separation. Often just ahead of control surface hinge lines, or on the underside of a aft-loaded undercambered airfoil. On small model airplanes that fly at VERY low Reynolds number, it is often beneficial to try to trip the laminar boundary layer right at the leading edge, or even from a trip wire suspended out in front of the wing. Actual transition will not occur until some point downstream, as the T-S waves amplify enough to cause transition. In all these cases, the higher drag of the turbulent boundary layer is accepted as a consequence of achieving better flow attachment downstream.
I remember the story that when the Rutan Vari-Ezes hit the scene many of the builders complained about performance and speeds vs factory specs. Burt always built his prototypes quick and dirty without a lot of perfection profiling. One particularly persistent builder with and amazing show-quality finish kept giving Burt the red *** about it at Oshkosh. So Burt finally make a deal with the guy in front of witnesses that if he could get the fellow's airplane up to spec before the end of Oshkosh the builder would agree to forever shut up. As soon as the deal was shook upon in front of everybody involved Burt walked over the airplane and started sanding the canard with 60 grit sand paper alternating 45 degree angles. The builder had a coronary but was reminded a deal was a deal. After Burt sanded the canard and wing until he figured the surface was to his suiting he turned to the builder and said, "There you go. Now go fly it". Part of the Eze lore.