I grew up never really seeing Mr. Hooper outside of the Christmas special. He died right before I was able to watch the show, so I'd admit some confusion the first time I saw it. Other than that, I'm glad Sesame Street, outside of child actors, Gordon, and Mr. Hanford, never recast any of the main human character when they got older and or moved on. Lesser shows would have recast the adults on the regular to keep them in the 20-40 year old range, meaning we'd have several Bobs, Marias, and Susans by now. This gives the show a healthy bit of reality, even though the ageless Muppet characters cause a paradox (and can be recast without much of a difference). I like that the humans were always coming and going because, well... that's what happens in real life. People move away, new people come in. Giving new characters to fill in the gaps left by older ones manages to unintentionally add a "make a new friend today" level a show like Sesame Street does great with.
As long as the newer cast members work well with the show and the Muppets, I'm always happy to see new faces.