First post, couldn't resist sharing my views on Mr. Rozen and as for why Gin-sama was left unfinished and is Rozen really as big a villain.
This may be spoiler-ish, if you have yet to see both Ouvertüre eps.
1 - Having seen both eps. of Ouvertüre shedding some light on the issue I would believe that as an artist and probably quite eccentric one at that, it is quite likely that the reason for Gin-sama not being finished before the other dolls, save for Kirakishou is as simple as frustration. Many an artist who fail to achieve what they have pictured in their mind grow frustrated and move on to working on their other ideas that fill their head for only a moment and could be lost forever if left undone. In Rozen's case it is likely that he failed at creating a suitable abdomen for Suigintou, being the first doll of her kind. Seeing as there's many other failed creations in Rozen's workshop and also Enju showed Jun some of his failed creations and even he was obviously saddened by this, we can conclude that it can be heartbreaking to not be able to create the perfection that such a doll would deserve.
2 - Rozen moved onto other projects probably because, as Shinku had said Suigintou's blueprints were lost. No idea as for why, but it is possible that Rozen was unable to control himself after many a failures and ripped them to pieces. But as he obviously had a Roza Mystica readied for Gin-sama and having told the other finished dolls about having already made her (not telling names) it is likely that he takes great pride and loves all the Maidens and planned on finishing Suigintou taking time to make her perfect as she deserves.
3 - Unaware of Gin-sama having become sentient without a Roza Mystica, seeing as he's immersed in his ongoing projects I'd believe he was quite shocked to find Gin-sama has been lost.
4 - It is likely that the Roza Mysticae connect to Rozen in some telepathic manner seeing as he was unable to find Suigintou until she had been to Sou-chan's N-Field. And seeing as he is somehow situationally aware of his dolls' doings and was able to find Gin-sama again after Shinku beat her in Jun's dream world to repair her. Also, seeing as how happy Gin-sama was to receive her Roza Mystica that was hers alone to begin with, I'd think Rozen didn't consider a missing abdomen to be of any consequence seeing as his (I'd call Gin-sama a masterpiece) Maiden was quite perfect enough already, if not in body, but in mind; being able to walk on her own and all. Besides, if Rozen wasn't able to make a good enough an abdomen piece to begin with, how could he conjure one up without any measurements when he gave Gin-sama her RM at such a short notice?!? They both seemed happy enough.
5 - Unfortunately it seems as though Roza Mysticae are a double edged sword: while giving the Maidens a powerful life force and personality, with it comes also the negative traits associated with any living human-like soul. Gin-sama was childlike, innocent and all, but not very understanding without her RM, such a pretty smile she has too... But once she received her RM she became to realize that Shinku's motivations might not have been sistership, but pity...
6 - Long story short, Shinku's Ego-nation going against Gin-sama's world of inferiority complex they end up crushing each other's "I like you" - factor. Something that must have been quite horrible an event for Rozen to witness. Bastard Bunny however seemed quite amused by this....
7 - EEEEP loooong first post, don't hate me.... *cough* Back to theory. I'd believe that both Rozen and Enju are being manipulated by Laplace no ma, but Rozen seeing further into the scheme refused to fully co-operate by having his dolls destroy each other. Realizing this, BB and Enju, who's obviously easier to manipulate, set out to crush Rozen's creations to steal the show and created Barasuishou for this end. Obviously Laplace wasn't counting on Enju's creation to be able to hold all the RM within to become Alice... but as for how the heck did he manipulate Kirakishou enough to become his puppet remains to be seen. Why else would we see Kira dancing with Laplace instead of Rozen at the end of Träumend
Unless Kirakishou's RM in the anime is used by Laplace in Barasuishou to strengthen it to be used in Rozen's creation.
8 - As for being able to manipulate the dolls to some degree I'd believe this double-edged sword of a Roza Mystica, somehow have their origins in Laplace. Shirosaki might be that mad scientist type of a person in the show, having found some ancient manuscripts for creating an ultimate "golem" (Alice) by uniting 7 aspects of a Roza Mysticae into one by some more or less obscure means involving dolls... or something along those lines. Having found his way into the N-Fields he sets out to create the 7 RM but not having the required skills to create dolls he manipulates Rozen and Enju to this end. Rozen making his maidens out of love, Enju out of envy. This would explain why Rozen's dolls have more of a good side, while Barasuishou is rather... soulless, probably just how Laplace would like all the dolls to be, just kill each other and be done with it. Bastard Bunny seems to enjoy the show anyhow even if his ultimate schemes may be delayed.
Think I'll end this here for now, as this is getting a bit too long