I suppose this might be tricky to do, programmingwise...but I'd LOVE to see a new tech branch that allows you to "shield" ships from enemy sensors. Starbase modules too!
You could stick 'em on your freighters to help them avoid pirates, on your fleets to stop them from getting intercepted on their way to target, and on your sneaky-deaky Influence Starbases to avoid diplomatic problems! Though the thought of spreading cultural influence via a space station no one can find DOES seem...a little weird.

Perhaps ships with a Survey Sensor suite could have an enhanced range of cloak detection. And it'd only work on the strategic map, I think. Until the final tech on the branch, where you get Tactical Cloaks that give all incoming fire a chance to miss your ship...but it replaces any other defense technology on the ship that has it.
And of course, you could stack multiple cloak units on a ship to increase their effectiveness. I just love the idea of parking Small cloaked sensor ships in enemy space to keep tabs on their fleet movements without them being blown up.
Anyone else think this'd add an interesting new set of tactics, and yet another "arms race" between techs (in this case sensors vs cloaks)?