Once an item (lets say the structures in the metal farm) has been scanned enough that there is no longer a benefit to scan that resource, the scan indicator should no longer appear, or maybe change operation. Overall, it is not a good user experience to feel a need to scan based on the cursor changing to the scan cursor.
A simple solution could be, when the scan cursor changes to show an item can be scanned, along with the Scan text info that appears, the text could tell us that the item is already fully documented.