IMO, I've seen file work added to knives with mediocre fit and finish, and to me it just makes the knife look that much worse. Then again, I've seen file work added to a masterpiece like those produced by T.A. Davison, and it just makes the knife pop that much more.
I think that if the finished work is sound, the file work, if tastefully done, can add a new dimension to the knife. You've got to be careful not to go overboard.
Then again, I've seen plenty of EDC's that would be ruined in my eyes if file work was added.
Very subjective topic, and everyone has an armpit....er....opinion.
--nathan