I hope you get a chance to read Carringer's Ambersons book sometime, because it's filled with some amazing revelations about the film. His "Oedipus in Indianapolis" essay contains some wild speculations that are not very convincing, but his analysis of the memos between Welles and RKO over the film's fate are very detailed and insightful. And you're right: the story of the film's undoing is so convoluted it is hard to know exactly who wanted what in or out of the film. It shocked me to discover, for example, that Welles himself wanted the following things OUT of the film:
1. Eugene and Isabel dancing in silhouette after the ball and most of the scene that followed
2. The famous "Iris out" the closes the snowride scene
3. Lucy and George's downtown walk, where she coldly wishes him a "splendid trip" to Europe.
4. Jack's visit to Eugene and Lucy's new home.
5. Eugene and Lucy's walk in the garden.
You may be right about the attempt at "concert symmetry" on the Hermann CD. But I was able to slow down the First Porch Scene to it's proper speed - thanks to a defective tape deck -and I think it sounds even more beautiful and more ethereal that way.