The entire point of Cute Jewelries 02 was Chieri trying to develop another image for herself, so at least she's trying to be a better idol.
There's also been a fair amount of 4komas about how she's growing into her cute bunny image, which also carried over to the drama CDs, seeing as how the clover-eating bunny joke has been mentioned a few times. Or how she's been in more variety shows lately, but has to persevere as an idol no matter how crazy it gets (which makes it all the more adorable at how overjoyed she gets when given the opportunity to try on a wedding dress).
So yeah, Chieri might be Yukiho 2.0, but she's not a flat character either. It's just really hard to fit those issues in with the rest of the group, probably. To be fair, they DID have one moment where she got to bond with Producer over her debut in the Nomake, but I haven't seen anything else since.
http://cgtranslation.blogspot.kr/2015/03/idol-mster-cinderella-girls-no-make-ep-9.htmlIn contrast, Miku gets a ton of development because her issues affect the rest of the group. Hard work not paying off? Character gimmicks being discouraged? Miku is a pretty good postergirl for those.
As for the rest of Candy Island, Anzu is hard to develop without completely betraying her character. Bribing her with candy to do work, or convincing her to do work now so she doesn't have to do more work later works, but putting any more motivation beyond that stretches her gimmick out too far. As for Kanako, afaik, she really doesn't have anything beyond making sweets and being a "nice girl". At best, she's only just now starting to notice her own sex appeal (read: boobs) after being too busy always thinking she's fat, so she does start to advertise herself as the sexy symbol of Candy Island, but that just says enough on its own. It's kind of sad to say that her claim to fame is sex appeal and making sweets, but that's how it looks.