Most of my pails are over 13 years old. I'm certain they have some scratches in them, but not enough that I'd worry about it.
I only ever scrub them with a soft sponge. I soak them overnight and most of the residue comes right off. I spray them inside and almost everything comes clean.
As long as you sanitize, or over-sanitize, there's no need to worry about nasties in your nooks and crannies.
I know a lot of brewers mention taking the spigot apart to sanitize. I never do that. The sanitizing solution goes to the same places the brew does.