Honda used aluminized/metalized paint and a very thin coating to preserve heat transfer to the air passing over the surface of the motor.
I learned from my days selecting cooling fins for power supplies that a coating has a very detrimental effect on heat conduction, and it doesn't take much to have a dramatic effect on heat transfer. Most were anodized aluminum for this reason and never painted. And black was the best color for emission and absorption. My concern back then was the junction temperature of the silicon devices. But, the cooling fins on our motors perform exactly the same function as the power supply cooling fins, and the transfer characteristics of heat remain exactly the same.
I would never powder coat a heat transfer surface without knowing the heat conductive characteristics of the coating and the thickness control method being used.
There are some coating materials that have conductive additives (metal flakes usually). But, silica flakes (also reflective shiny) do not conduct heat very well.
We have air cooled motors, and when it matters most (hot temps and hard running the motor) is when heat transfer is needed the most. It does matter, as there is no regulation of delivered air volume to take the heat away. And once the oil temp tolerance is exceeded, engine wear is soon to follow.
Anyway, adding cooling fin (and engine body) insulation is equivalent of stagnating the air flow over the engine. Does anyone really think this is a good idea?
Now, perhaps to compensate for thick insulating powder coating you could add a fan out front to ensure adequate compensatory air exchange... Not a trade off I would make, though. But, if slow moving parades (or traffic congestion) are your thing, it might allow your engine to survive.
Cheers,
