I just watched the entire LOTR on blu-ray over the past week and was thrilled to see that certain characters and scenes (that were already very good) were improved even further after having watched The Hobbit: An Unexpected Journey.
Every scene with Bilbo and Gollum, the various references to Bilbo's adventures, Gimli's animosity toward Legolas and elves, Galadriel, Elrond, and Saruman, Bilbo declaring that he was "ready for one final adventure" after his iconic announcement regarding his *first* adventure in AUJ, all of it. It made a series of amazing films even more enriching and poignant.
I can't help but notice the contrast between it and The Phantom Menace, which made every single character that also existed in the OT slightly worse (save possibly Obi-Wan.) I can't *wait* to see how the entire six film Middle-Earth saga plays when all is said and done.