I guess with "proper" tools , industrial grade, polishing isn't bad. I've seen carbs polished to mirror finish. I don't have patience to do this. Plus my cover I cut and filled the water nipples, polished the center, painted the logo.
The way the cover is cut away for pimp cover it's ugly no matter what you do.
As to that crack, I'd have used JB Weld with fiberglass cloth on inside, notched crack on outside , fill, sand, paint, done !! FTW !!