You do NEED SoB for S rank in MN, as far as I know.
The more aggressive you play, the better you'll do and the more fun you'll have... UNLESS you are going for karma. The SoB restriction rewards patience, not aggression. It's also about as fun as watching paint dry. The Karma grinding is just that: grinding. It's not fun and it doesn't test how good you are at surviving and dispatching the enemies in the game. Rather, it tests how good you are at abusing the games mechanics to get awkward, consistent, high-karma points.
@Angelo: Again, that's from end-game, where he's always maskless. I am fairly confident we won't get a selectable maskless costume in RE or DOA5, as much as we want it.