I consider most marks on a sewing machines to be battle scars. They're often honestly won, and a record of what they've gone through. There are very very few machines out there without marks on them, they were tools, not collectibles when they were new.
It's possible it can be polished out, or touched up, I can't tell what the mark is from here. If you're sure you can make it better than it is, not worse, I'd say go for it, that may not be an easy task though.