I replace my helmet once a year, or every crash whichever comes first. Luckily there has been no crash in a while. But I keep the old one and usually the one before that.

It's nice to have a back up for a guest helmet or just a day when you can't find the new one .... I'd keep it.

The finish sounds like cosmetic damage only, nothing that would hurt strength/effectiveness. Enjoy your shiny new helmet but keep the old one for a while.