I was struck when reading ADF's Star Wars novelisation that characters like Red Leader and Gold Five (okay, so the colours and numbers are different in the book) are clearly veteran pilots and mainstays of the Alliance's teams of fighter pilots. I would love to see more of them. Biggs and Wedge could be introduced in earlier episodes and characters like Mon Mothma, General Nadine, Admiral Ackbar and General Rieekan could all crop up. Also Bail Organa could be seen and Episode III could see him giving his young daughter her first assignment for the Alliance!
As I've said previously, I like the idea of Leia stepping into her father's shoes as one of the leaders of the Alliance following his death on Alderaan and BY. I imagine the other leaders being concerned by her youth and inexperience and send her to Hoth with Rieekan to see how she does. This leads to her desperation to impress with her leadership skills and her bitter disappointment when the base is discovered, attacked & lost. I think this is why Leia is so angry in ESB. It doesn't help that she's stuck on a small freighter on the run from the Imperial Starfleet with a wookie, a camp, shrill droid and a scoundrel that she finds irresistable, despite herself.
It occurs to me that it may be Bail Organa who is most convinced that the Return Of The Jedi is necessary to the Alliance's cause. He could be the one who tries to trace the last remnants of the order and discovers that his old ally, Obi-Wan Kenobi is holed up on Tatooine. Maybe the rest of the Alliance's leaders are less convinced that (a) there are any Jedi left anyway and (b) they would be any great help. Maybe they think Bail is obsessing over something peripheral when there are greater tasks to be addressed.
Little do any of them know that Obi-Wan is watching over a very special farm-boy on Tatooine who just happens to be the son of the legendary Anakin Skywalker....