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.
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.