A good question OP. I move on despite the fact that I can still be paid for my efforts, albeit not as much. I'm a bit tired of the competition that goes with ED at the moment: be first to do this, deliver the most of that (etc.). It's all down to the mentality of the player of course, because we are supposed to get out of ED what we want from it. I try to ignore this aspect of ED, but yes, I avoid previously scanned systems and move on. (I even skip those that contain ice worlds.)