Currently, I don't see the point of sensors on most ships.
What I generally do is create "sonar buoys", basically cargo ships with nothing but sensors on them. A few of these can see who quadrants of a medium map, ensuring nothing gets through my territory without my notice, and its far more efficient than placing sensors on all of my ships.
In addition, because of the buoys, I never feel the need to get strong sensors. Even the basic ones provide plenty of distance when massed on a cargo ship.
I think sensors need a change to make them more generally useful (some combat bonus), or allow only so many sensor modules on a given ship.