I think the only reason why the flashbacks in the show work is because they somehow inform upon the actual storyline. Same with The Godfather - in Saga form, as a straight story, the scenes with Michael as Boss aren't half as effective without the flashbacks, and the scenes of Vito in Sicily aren't either.
That's why I've always been against a prequel. There's only so much you can do; curiosity in already-established characters' earlier lives may serve in some way, but how long can you strain dramatic irony?