If Oreki hadn't changed, if he still followed his stated philosophy of, "If I don't have to, I won't; if I have to, I'll do it quickly," then he wouldn't have gone to Chitanda's festival at all. But he did. He became less selfish and opened himself up to new experiences.
As for the movie arc, Oreki changes, but not necessarily for the better. He's hurt by the experience, and tries to shut himself off from everyone. Not because he's lazy, but because he thinks he's useless. Episode 11.5 makes that more obvious, but it's still apparent from the material. The way he dives into the movie mystery is totally different from his apathy at the beginning of the festival.
In Chuunibyou, Yuuta's only character development is related to his relationship with Rikka, she ends the show pretty much exactly where she started it, and Isshiki and Kumin basically never changed at any point.