The numbers are just for relative and subjective location on the ship. All DVs are the same as are all PVs or any other class of stateroom. V and DV are the same room size and layout just slightly different ammenities. Some people like the higher floors as they are closer to the pool, Explorer Lounge, and some people think the view is better (and the higher rooms are away from the life rafts). Some like lower levels for less waviness. Sane with mid ship- less movement. Worth it is subjective- PV has significantly more room and storage but DV is a very nice room. As you go up in category you getting more advanced booking for excursions and dining but many people say they got what they wanted regardless.