my thoughts are painting wont affect heat much at all. it will likely be slightly hotter. but unless it's a thick epoxy coat or something it's not a big effect. I mean the a35's all came loaded with thick black paint and they're great regardless.
vapor blasting is nice for nice things but not exactly cheap or quick. probably cost you 50-75 bucks which at that point you could buy a 2 brand new heads or a performance one with custom cut squish.
but yea, go ahead - paint's a good freshen up for appearance if you want it pretty. polishing is a nightmare between all those fins etc, but if you got time to kill it'd look nice and could work marginally better.