Isn't Mars known for extreme winds and dust storms, which seem like quite the challenge for an ultralight drone resting on the surface, let alone flying autonomously?
So far the fastest winds observed on Mars are about 30m/s.
So, the thin air that makes it hard to fly on Mars makes it safe to stay on the ground.
Running the worst case numbers, 1000 10um particles per cm^3 adds up to about 1/3 the air density. Realistically it's maybe 10% of density increase.
“The addition of water vapor to air (making the air humid) reduces the density of the air, which may at first appear counter-intuitive. This occurs because the molar mass of water (18 g/mol) is less than the molar mass of dry air.”
(Not sure I like the language above but that’s how Wikipedia says it)
Is this potential effect accounted for in your numbers? I.e. What happens to the molar mass of Martian atmosphere when Martian dust is suspended in it?
At any rate, dust is bad for the moving parts of flying machines.
Dust doesn't have a meaningful vapour pressure and can't influence air density this way.