I've used ELNIT on my combat ships, cruisers and battleships, all of which fought in missile and beam combat with aliens, and I've never gotten anything from it. Staying within range of enemy ships for 100 days is not something that usually happens in my games. Even if you cumulate all the combat together, by the point it's done, it does not matter much anymore, because you've dealt with these ships enough to know what they're made of.
Also, the lack of feedback on its work makes it even less desirable on my ships.
I'm yet to build a dedicated ELINT ship... feel little need for it.