Well, I suppose the problem started with Qui-Gon.
The question becomes "Why doesn't Qui-Gon come back in the same way that the Obi does in ESB and ROTJ?"
In fact, why doesn't ANY Jedi show up later in ANY of the films?
"There is no need to explain anything about the force ghost or mention Qui-gon. It dumbs down the Force for the audience, and makes it less mysterious."
I guess I disagree here. Midichlorians dumbed the force down. Returning in qhost form is interesting.
"Let the audience draw their own conclusion as to why Jedi can come back as force ghosts."
But that's the problem. Out of hundreds of Jedi we see in the saga, only 3 return? The questions is "why?"
I personally think that is something that needs to be explained.
"This would remove the need to insert and mix dialogue from other films that does not sound good and stands out very badly."
Ouch. The clip Good Musician posted was (he said so in the same post) raw and unfinshed.