Adding my 2cents... sound/music can add a lot. The thing is, there's only a few who really mastered the art of adding a good score. Most of the VN's which have music fail to deliver that. When done right it adds a great deal to the power of immersion, if not then the "Mute All" is usually the first thing you reach for.
The argument that sound isn't important because it is a VN completely misses the mark... Even the argument that Charlie Chaplin and the likes had great success with their silent movies doesn't cut wood, coz even they had music added to convey the atmosphere. So if that were true, tv shows and movies wouldn't get great music scores added...