In the course of a TV show, especially one that's over 40 years old, recycling episodes is only natural, though they've done it a remarkably high amount of times the last few seasons. Especially the guessing game crap.Either way, the movie will more than likely draw on some sort of past formula... I mean, look at the show itself, HOW many episodes have we had involving a chicken thinking Rocco is an egg? How many times has Oscar launched something from his trashcan like his own show or something, and Telly ends up being his sidekick? How many characters have suddenly taken on a reporter guise for a day to report on various similar events happening on the street? Even 2001 wasn't the first time Sesame Street was hit by a hurricane apparently.
There's a Japanese kid's cartoon series called Doraemon, and that's been on the air since 1979. They ran out of plots, so they started just redoing old episodes many years later. I don't mean recycling plots... completely, legitimately taking old episodes and doing them a second time, maybe adding something here and there (celebrity cameos or something), but they are the same exact stories revolving around the same exact gadgets. People who have seen those old episodes will know that they're remakes, but the demographic that the show's intended for won't.
As far as Sesame Street doing a movie, while the show has done everything, they haven't done anything that's too ambitious that can't be done in the matter of a single episode, a 2 parter, or maybe a week long story arc (something they don't even attempt anymore). Plus, the film doesn't have to have educational content (other than the fact that storytelling demands lessons and morals), so they can go off menu for a film.