There's been some work on reducing drag on boats and planes with small surface texture features. (Google "Drag Texture Americas Cup")
One speculation I've seen on that subject is that the drag reduction is due to the relative sizes of the texture features and vortices formed. (Haven't looked enough to know if there is anything more definite than speculation.) Did find, that for boats, smoother than 400 grit doesn't seem to affect drag.
I agree that at some scale roughness probably doesn't increase turbulence. (at least in a manner beneficial to cooling) What that scale is, is the question.
In looking at the info on boat hulls I saw it mentioned repeatedly that surface tension doesn't play any significant role in drag.
I'd guess the 'minimum water drop radius' is probably not relevant, but I'm way out of my league with this stuff.
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