I'm not sure if anyone has mentioned this, but if you look at the movies alone just as the movies, I think they'd have to add either a sidekick of one hell of a villain because Bale's Batman can't carry a movie on his own. He tried in Batman Begins but had to be heavily supported by Alfred and Lucius, they made it much more interesting. Villains were bad this time around, but it is forgivable, this one was about Batman's origins.
In Dark Knight, Alfred and Lucius were toned down but Gordon was given more screen time. Then you've got Dent/Two-Face who was a major part of the plot direction, and the Joker who was not only a fan fav but also was the overseer of the whole show. They killed Dent (real shitty job too), and Joker wont quite be the same with Ledger dead, so they'll need a new crop of villains to keep things entertaining. Regardless, with all this extra support just hammered down how boring Batman is on his own. And with Bruce Wayne getting more insane as the series goes on its about time they give him an anchor, they can't use Rachel anymore either.
All in all, a Robin will help, especially Dick Grayson. Bruce Wayne takes in Grayson as a chance to redo his own life vicariously. Dick's parents were both murdered, like Wayne's, and this creates a lot of frustration which if not properly guided will ultimately lead to making another villain for Batman to have to fight. This is also a good time to show the gangsters again, as Nolan seems to love them. They kill Grayson's parents and then we can move on to something other than cleaning up the town that the last two have been about.
What this does to the movie franchise is brings it back full circle to the beginning of Batman Begins, but also kind of makes it into the same movie. Except, that at the end of Dark Knight, Batman makes himself out to be the anti-hero so they could add Robin as a way to redeem Batman in the eyes of the population of Gotham. It also shows how Batman has matured over the years and still lets the primary theme of the trilogy be revenge. 1st time was Batman's, 2nd time was Dent's. 3rd one can be about Robin's struggle to get revenge while Batman is trying to keep Grayson sane unlike himself. Again, they have screwed a few things up by having Barbara Gordon shown as a little kid because she was Bat-Girl at the same time Grayson was Robin. Unless they have a new Barb Gordon show up who was at boarding school the last two movies or something.
Who knows really. Robin is a great character if done right, but hasn't been done right on screen and most people still have the 60's version in their head. Burton was able to change people's mind (general population, not comic book fans) about Batman but when Forever and Batman&Robin destroyed that series they did so without making Robin cool.
tl:dr - didn't miss much. Robin can work, movies need "something" cause Batman can't carry a movie.