Too much of anything's annoying. I really hated when Disney forcefully marketed Winnie the Pooh over the characters Walt actually took credit for creating. The loveable character was lost in a sea of ugly old women sweatshirts and Pooh dressed up as one of the 101 Dalmatians plush toys. You literally couldn't even find Mickey at a Disney Store. But the projects (most of them anyway) made the character shine during that period.Maybe too much of Elmo can annoy people? Nower days it's nothing but Elmo lots of the times and no stories of the other Sesame Street characters.
I feel the same with Elmo. Sure, now they took the hint and we're seeing more Cookie Monsters, Ernies and Berts, and even Big Birds in our Sesame Street merchandise. Elmo does have a ubiquitous presence in the show still... but other characters are catching up.