I didn't think much of it when I first watched it, but thinking back... I think it actually provides an interesting twist and a different character development. Usagi mentioned that Saphir was insane in the manga (I think) after she talked to him alone while in the Black Moon spaceship thing... but that was never explored, was it? He was insane in what way? He'd actually always struck me as the only sane/logical one of the group, the one not driven by emotions. But then the musical twists that cold logic, strips him of all emotions completely, and pulls all those characteristics to the extreme. And what you have is Musical!Saphir, who could replace his own brother with a droid and not a single person actually realized it, not even the droid himself.
Seeing a more "humane" version of "Demande" was interesting too. They played with switching around the brothers' roles a little bit and made him to be the one more likely to achieve redemption, and that's not even a real human being (it then makes the interesting point of droid being able to have human emotions, even ones that may or may not be the opposite of what their actual "model" might feel. Basically it opens up interesting possibilities to think about.) Parts of it have been done before (in the old musical, in the anime, Demande was similary "redeemed") but they're doing it in an entirely new and interesting way.
It seemed like a pointless twist in the beginning, but it's actually not really.