I'm sure they could've done a corridor shot on greenscreen (heck, they still might), and they absolutely could've redone all the sets as they were. Part of the idea in doing this as a CG series was to do stuff they couldn't have built physically. Personally, I always wondered exactly how they got the Vipers from one pod to the other in the Miniseries, and it irritated me that in BSG's haste to not be Star Trek, we never once saw an elevator in six years. And no one is going to be walking an injured crewman from engineering to sickbay across a mile of corridors and down thirty flights of stairs.
Did they go over-the-top in making more elaborate versions of the old sets? Yeah, probably. But as Drexler pointed out, they made sure to use the original sets as a starting point, so you could see where they line up with the versions in B&C. As far as near-unrecognizable hand-waved "refits" of sci-fi ships go, it's a lot more faithful to the original design than the U.S.S. Enterprise from the Star Trek movies was to the original TV show.
It's interesting to mention "Forward Unto Dawn," since the only thing FUD and B&C have in common are the distribution method and the rough release date. FUD was intended to be a more character and plot based exploration of its universe, to flesh out the action-oriented take the video games provide. B&C has the opposite aim, to provide an action/adventure story of the BSG universe to counterpoint the more cerebral and deliberative tone of the parent shows (remember how there was exactly one space battle in all of season 3)? Also, not negligibly, FUD had a $10 million production, while B&C was made with $2 million. For comparison, "The Lost Tales," the Babylon 5 direct-to-DVD project five years ago, also had a $2 million budget. Now, they did get a corridor, but not much else. (That budget is also why I forgive them for the candy-colored, bloom-and-flare art style. They don't have any live-action to match, like when they put in a centurion or did a set extension on the hangar on the old show, nor do they have a giant James Cameron production apparatus to get their CG perfect in isolation. It's understandable that they'd use every dirty trick in the book to set the actors into the backgrounds, even it has the effect of making the real stuff look animated rather than the animated stuff look real. Still, I like animation. Clone Wars, good stuff).
Right now, I have a feeling that my biggest issue is going to be the plot structure necessitated by developing the movie as a seven-part serial. It's like commercial breaks on steroids, since it seems part of the the aim was the make each section kind of stand-alone. I don't know if it'll be possible, since we've only seen a quarter of it so far, but maybe the longer TV and DVD versions shuffle some scenes in the edit so the plot isn't so obviously broken into discrete chunks.