Yea, it'd be a much better "creep area" effect, like the Zerg have in Starcraft. When you build structures as the Zerg, the creep area increases around the buildings, covering the terrain. Why isn't the creep in this game more like that? It would help builders know how far they can build.
As for the Humans, this idea can be used as well, except, only when you have a construction kit. If my idea is implemented, if you have your construction kit out, a transparent sphere is drawn around the reactor and repeaters, to show how far the power is going, like the Protoss Pylons do, in Starcraft.