As i posted, you can add more components from the same family, but the only advantage you get is that you still have the bonus when one component gets destroyed, which is not very likely due to its size compared to the total ship size, usually 300kT+. And yes, i know that 15% to hit compared to 10% to hit is a 50% increase, but it usually wont happen. 50% to 55% is more likly, and given the research and ressource expenses needed to aquire/construct elite sensors or ecm i would prefer making more ships to simply outgun the enemy
Of course its always the question how one is playing. Some want a few state-of-the-art ships, other go with masses of seeker-throwers, where hit% doesnt matter at all since you try to attack out of enemy range.