Stock rocker polishing

I wonder if there a benefit in polishing the stock roller assembly and rocker arms for less friction?

Or even use some bronze inserts at the rocker arms, again, to reduce friction.
That's what roller rockers do, reduce friction. Reduced friction at the rockers will not increase power measurably. What roller rockers will do is allow you to run stronger valve springs without breaking rockers or shafts, have less strain on the valve stems, and have adjustability in the valve train.
polishing the stock roller assembly

Not aware the stockers have roller anything in the valve train. You referring to the stock rocker assy??
I doubt that bronze bushings would survive w/ the very small support area that the stamped rockers have.