I wouldn't be too hasty about the dust.
I've seen some tiny little craters, a few inches across, in recent Mars pictures. Unless they're only a few years old, I'm not sure things like impact marks would get covered by dust all that quickly.
At least in some of the areas we've seen with the rovers, the mechanism seems to be "dust on, dust off" depending on what the winds do. Some places, like the bottoms of craters, do seem to accumulate it.