I do not agree at all that it is not useful but even if true the PR in itself is likely worth it, both for getting more attention to NASA (IE. budgeting) and for sparking ideas and dreams.
I'll gladly change my mind, what is it useful for?
On your other point, I'm sure many people find it fascinating and are inspired. However a young geologist or biologist might not be inspired to start a career at NASA. Another point the author of the article above makes it that in the ~2 hours of live coverage, 6 seconds were spent discussing the rovers instruments.
As for budget, this is also dangerous; after all, if the next funding round comes along, anyone who does not like NASA can have an easy argument that the $80M on the helicopter are wasted and did not produce any knowledge about Mars or the universe.
It's useful (if it doesn't die) for scouting. From above, it will have a better look at the terrain, helping mission control do path planning and terrain/risk assessment. I have no information telling me that's going to happen, but this is my fairly educated guess as to how the drone could be used.
Ok, that could be a use for it. They do have satellite images, but I guess those are much lower resolution and a better satellite would probably be orders of magnitude more expensive.
