And while I do indeed support expanding Qui-Gon's role, it would be in a different way that Obi-Wan's life after death, as MTHaslett already pointed out. The problem with what I think you were getting at, TM, was that there can be no conversaions between Qui-Gon and the characters. This puts him in a very similar position as Obi-Wan in ANH after his death. He communicates with Luke in extreme moments, but they aren't chatting it up and we don't have Luke questioning how he's talking to him. In fact, Luke seems to not believe it himself at first. Here are some places I think dialogue from Qui-Gon would be approriate and meaningful:
-At some point during the space battle, when Anakin fires the torpedoes into the reactor for example, have Qui-Gon in his head: "Concentrate on the moment. Feel, don't think. Use your instincts." Qui-Gon is straddling life and death here, so this could be interpreted as either a rememberance (he told Anakin this before the pod race), Force user-to-Force user communication (Luke and Vader at the end of ESB), or advice from the netherworld (Obi-Wan in ANH).
-When Obi-Wan is hanging in the pit, have Qui-Gon is his head: "Always be mindful of your surroundings." Then he remembers Jinn's lightsaber is still there and leaps up to kill Maul. That could be interpreted as the latter two options from above.
-I thought about having Qui-Gon die after "Promise me you will train the boy," (assumming you would keep that line), then have "He will bring balance. Train him," echo in the long shot, in Obi-Wan's head I assume. But that might be a little weird.
-I mentioned this before, but perhaps have some of Qui-Gon's tone poem in Anakin's head at the funeral. "It will be a hard life. One without reward, without remorse, without regret," etc. This would tie-in with the dream in your Episode 2, but again it might be a bit out of place.
-Qui-Gon dissapearing in the fire? Again, logically there would be some kind of reaction/response, so I'd say leave this as-is.