I was also excited about it, however an article critical of various points of Mars 2020 damped this quite a bit [1 (in German)]: Does the drone actually have any scientific relevance? I'm even doubtful it answers relevant engineering questions. I mean, it was tested in a pressure chamber already simulating mars atmosphere and gravity, we know it will work. The only question seems to be: Will it fail because of some engineering oversight or hardware failure, or not? There seem to be no scientific sensors on it at all. This 'commodity hardware test' could also be done with just the processor and monitoring, without the helicopter part. Looking at it like this it seems like mostly a toy or PR stunt, but one that takes $80M and space on the rover away from scientific projects.
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.
[1] https://www.golem.de/news/perseverance-diese-marsmission-hat...