I know that was probably more of a joke, but I never thought of adding Elmo's World as a way to save money from new inserts (they do still have to come up with 15 minutes of material for Elmo's World, even though they initially repeated the same one all week). After all, there's several season 30 inserts that did not air until the episodes were rerun (and re-edited) during the summer (many of which never showed up in an original broadcast cut). And over time, there's been more and more inserts produced for the show that have never shown up on the domestic Sesame Street but have shown up internationally (quite a few made it to Play with Me Sesame, some have shown up online with the original English audio).
And even if it was too expensive to do a lot of new inserts, they had 29 seasons worth of existing inserts they could have filled those 15 minutes with. There are a lot of classics that had not been seen since the late-1980s or early-1990s that most likely they just hadn't gotten around to re-airing for years (and maybe they still wouldn't have been shown, I'm not sure if they kept close track of how often segments had aired).
Reminds me that I had been toying with the idea of taking some season 30 episodes and making a list of segments I would have liked to have seen if they didn't suddenly have to devote so much time to Elmo's World.