I have several ancient lenses that are all scratched up. Some have marks left from fungus and haze. I still shoot them, and still get great photos from them. I might be a bit more careful about lens flare with the scratched up ones. But otherwise, I don't worry much. If anything, they add character that you can't get from a modern lens in pristine condition.
As they say, sharpness is overrated. Once you get good at photography, you quit worrying about lens sharpness, scratches, the latest gear technology, and all of that jazz, and worry about things like composition and intriguing new subjects, angles or techniques that you've yet to explore. Worrying about gear is what amateurs do. Worrying about photographs is what professionals do. Do yourself a favor and quit worrying about the little stuff now, and get focused on the hard stuff, like how to photograph something that's been photographed a million times before in a new and compelling way.