I would like an added function that displays the effective 'line of sight' of ships and stations. I enjoy playing on the 'Clusters' maptype, where the island hopping-style warfare keeps things quick and interesting, but I also like to place small 'Eyes' outposts, fitted with nothing but shielding and point defense, to allow me a few extra moments of warning about enemy ships approaching my systems. If there were an actual mechanic for sight range, I feel like the issue of outposts and the like would have more purpose. As it is, I guess at more or less arbitrary distances and hope they catch whatever flies between. 12 AU's seems to be a good distance, in deep space. In addition to this, it would make ECM-type equipment have a much broader use. Now, you could sneak ECM-fitted ships past enemy system defenses, by skirting their sensor ranges. Scouts with ECM hulls parked so far off the orbital plane that the broad ring of fortress-stations can't pick them up, deftly skirting the delicate web of sensor stations spread out across the edges of the system, searching for sneaky little ships, just like theirs... Another addition may be specifically sensor-boosting equipment, that allows you to penetrate ECM, or expand the range of detection.
I feel that this would add a good layer of depth to the game, allowing more strategic options, and also giving at least slightly more utility to fixed defenses.