Waste of time. Flow is in the shape, not the finish. In fact if you polish it too well you could seriously hurt power because fuel that hits the walls would have greater tendency to "ride the wall" in liquid form rather than bounce off and stay in an atomized suspension. And if you are talking about hogging it out, I would advise against that too. Unless you really know what you are doing you risk making the intake lazier (increasing volume without significantly increasing flow) and reducing velocity.
Knife edging the plenum divider will gain nothing if it is a full divider. But even if it is a dropped divider, I'd be willing to bet that gains (if any) would be completely unnoticeable.
Now it is never a bad idea to port match the intake to the heads, though.