Good point. People had been feeding off Lucas' films for years before coming back to make more films. Then when he dips from his own well and people cry "Plagarism! Rip-off!"
The sad thing is that with the last two films, Lucas pushed the bounds of movie-making by creating and rendering his backgrounds and sets digitally. It's not new to have digital effects, but his company, ILM, keeps pioneering the effects that are used and broadening the tasks for which such effects are used. No one notices this.
Another sad thing is that NO ONE even remarks on the music that John Williams has created for this series anymore. Apart from the effects, it is one of the facets of these films that is consistent in its excellence. His music is the mortar that holds these movies together and hardly anyone cares.