You can swap out the pistons to the new k24z3 pistons. Did you get the right pistons for your block? There is a A and B set unless you got the over size pistons which won't matter.

Adding slightly more comp will only benefit with other mods done to the car. i.e headers/intake/exhaust and etc.

Is it a worthwhile mod to a stock engine? I would say no... the time and labour isnt worth it.