Jung would provide us with more juice, I don't think you could argue that one, and that is a big part of what we are missing at the moment, but you do bring up a good point that Josh Smith has done a tremendous job filling in and being very productive. It's fair to wonder HOW much better having Jung would make us. I think he's probably worth between 1-2 WAR at this point in the season. I think he was due for a big year.
Edit: as I say that Josh Smith currently has a 1.7 WAR....so being better than that would be a huge start and probably MVP territory.