Lucas is always gonna try to do as much as he can with the technology he's got. The guy's always been at the front in terms of this kind of development in movies, so it's no wonder he likes to play with all his toys, so to speak. Look at ANH - compared to the other films in '77, I bet I could come up with about 100 shots that were mainly for 'wow' factor and were strictly speaking unnecessary, but that's Lucas for you and he's always going to push the envelope as much as possible. At the moment, if he can do it as an effect, he'll do it as an effect. The fact that he's now recording digitally makes this process even easier to integrate with the real footage.