i seem to recall david vizard saying there was a performance advantage to polishing an intake manifold.does this help it to cool off quicker?

No, polishing an intake manifold actually will hurt it's cooling capacity.

If there is a performance advantage,you will never,ever see it in a timeslip..waste of time and frustration IMHO and experience.

There is supposed to be an advantage to Jet-Hot coating the bottom and top of the intake to keep the air cooler, but that would be pricey. I don't see how polishing would help.

Helps keep it clean is all. Think of it, you'd want the heat of the manifold dissipating off the top of it wouldn't you? Therefore a thin flat black coating would be best. Polishing would tend to retain heat. But differences are likely N/M ( not measureable).