Professor,
Very true, however, with painting the cylinders black first, I've never had a problem with the polished fins causing overheating problems.
On the heads I've polished, only the outside fins were polished. The ones over the combustion chamber were left rough (with only the very edges being polished).
I am a little leary of those chrome plated heads I've seen being sold. The extra layer of copper and nickel that goes into the plaiting process can't be good for heat dissipation.