Even this relatively "inefficient" quadcopter (8 rotor) design could cover dozens of miles (~60km, more than any Mars rover has ever done in its entire mission) in a single hop (which could be recharged by the MMRTG in a single week-long night), although prudence suggests shorter hops at first. That means in principle over its ~10 year lifespan (assuming it can last as long as Cassini did...) it could nearly circumnavigate the entire planet (diameter of ~5000km, day period of about 16 Earth days) while visiting dozens of sites. Granted, range will likely be much more modest as the mission operators will be focusing on not losing this valuable asset, but it shows just how powerful the ability to fly could be. It can visit more sites than all the surface robotic missions to Mars combined. In that sense, it's a fantastic scientific value. And I think the public will absolutely love it.
Information from the Dragonfly proposal document: http://dragonfly.jhuapl.edu/News-and-Resources/docs/34_03-Lo...