Looks like my 1000th post since the SM crash is going to be a quick review of Thermodynamics (yay!):
1: Few gains are to be had by cooling the relatively short intake piping going into your engine (especially NA). At WOT, the air is moving fairly quickly through it, and only a small portion of that air is actually hitting the walls of the piping (unlike an intercooler where the air is hitting all kinds of extra surfaces). But even if you were successfully able to drop the temperature of the intake piping/manifold by 20 degrees (which I find highly unlikely), you probably would not notice any power increase unless you were running right on the edge of knock and that small change in temperature prevented the ecu from pulling timing).
2: The underhood air temperature is roughly 150-175 degrees. I'd estimate the manifold & piping are around 175-185degrees (just slightly cooler than your engine coolant, and moderately cooler than the block itself). But since metal in contact with other metal transfers heat fairly efficiently (block/head ->manifold ->NA "Y" intake pipe), the manifold and piping are actually giving off heat into the engine bay (especially on a turbo car where post IC temps are still warmer than the underhood temps).
2a: Since the pipe is actually giving off heat, any attempt to insulate it (ceramic coating, powder coating, wrapping it in foil/waterheater wrap, etc) will actually make the intake hotter. But again, according to point 1, the actual difference this makes is minute so it really doesn't matter if you do powdercoat your piping...
2b: Polishing the pipe will have the same effect, but to a smaller degree. You are removing surface area (the extra ridges that make the surface rough) with which the air comes into contact to transfer hear.
If you want to lower your air intake temperatures from 150 to 90 degrees, cut a larger hole under your headlight and make a custom cold air intake. But even then, you probably wouldn't actually feel the difference in power (maybe a slight difference on a turbo car because of the heat produced from compressing the intake air)
Edit: If you really wanted to cool off the intake manifold & piping, you could try slipping a rubber sleeve over shanks of the the intake manifold bolts/studs and using a nylon washer. This should insulate the manifold from the head -- at least for a short time. Don't forget about that intake manifold brace that attaches direct to the block...
