Go ahead and polish your piston crowns, a nice mirror finish will help limit carbon buildup and also reflect more heat into the combustion chamber keeping the piston a little (probably not much, but won't do any harm)
As far as polishing the con-rods, I haven't heard of anyone busting a rod, usually the first thing to go on them is the rod-bolts, so might be a better idea to uprate those, ARP make (if my memory serves me) make good ones.
