I been thinking a bit more about this and thought that as well as the length of the trails they could also be colour coded in some way. Not sure how though? The trails would only be visible to the player if they had researched the radar array or something similar and had put these on a planet or starbase or indeed a ship that he/she owned.
So if the radar array technology had not been researched then the visibiliy would be very limited to say 1/2 to 1 sector.
Then the higher the radar array tech level is that has been researched the farther you can see!
Are radar arrays or something similar in the game already and if not how easy would it be to add? And if it was added would it enhance the gameplay? Personally I think it would.

Am I making sense?