Enemy ships probably shouldn't be able to walk up to your front door unnoticed.
Not if you take precaution.
How about deploying Listening Posts/Spy outposts along your borders?You don't magically see what's inside your own borders. If you can't bother defending your way home, the game shouldn't do it for you.
Crippling your eyes should be an invader's or intruder's first order of business.