If someone is talking about a port and polish, it usually involves the head; cleaning up the air passages on the intake and exhaust sides and the bowl area. It will flow more air more easily. If that indeed what he's talking about then it has nothing to do with the pistons or boring the block. Since you have a completely stock Evo, then maybe try some easier upgades first; exhaust, fuel upgades, boost control, and tuning. Try the bolt on stuff and see if you like the increased power before you go removing the head.
Cams are usually done after the mentioned bolt on stuff and they all make power by flowing more air though the motor.
More air + more fuel = more power, but less fuel milage. We can't have it both ways.