Has anyone ever smoothed their rear bumper?

First it was the side strips bugging me but now its that stupid line in the rear bumper. My rear bumper needs spraying. How much would I expect to pay to have the line smoothed in?

Or am I being stupid and its there for a reason?

I am sure somebody has done it, it'll need to be plastic welded then smoothed over, then sprayed.

Duggie had his bumpers smoothed over