heres another way to look at it, the golf ball is dimpled because fluid dynamics show that the dimples create pockets of air. these pockets create a lubricating effect reducing friction. thats because air stays in these dimples and doesnt touch the plastic case of the ball.

translate that to electrodes, if its rough there will be a place or pocket for air to remain trapped thus blocking water from making contact with the electrode, no contact no production. a mirror finish does reduce surface area but it reduces pockets.

if a pocket is visualized as a U shape then you can see how polishing the surface would reduce by a factor of 50% but considering that the pocket looks like 0 because air is trapped and water cannot get in you actually gain 25% surface area in the real world.

better to gain some then lose all right?

i think by mirroring the plates it will increase current draw atleast for the same given electrolyte.