I have heard and read that V-Power contains a UCL, which may explain why some folks are seeing increased fuel efficiency.
As for fuel being enriched with Nitrogen, that just doesn't make any sense to me. Nitrogen is an inert gas and has zero BTU value. Nitrogen can be compressed because it is a gas, but it is not combustible. We use Nitrogen (N2) to drive control valves, to supplement our plant air system during periods of low pressure, to purge amine contactor towers, and to air-free process equipment at the refinery where I work. Shell's claim is bizarre to say the least, unless they have figured out a way to use N2 to create some kind of reaction.