As I've said many times before, when the documentary on the DVD cuts to a CGI cityscape as George talks about using real locations in 1970, my jaw dropped.
If Lucas really wanted those kind of shots back then, he probably could have gone with matte paintings. Guys like Albert Whitlock were still practicing their craft in the industry at the time.
As it is, those sprawling cityscapes undercut the claustrophobic underground vibe.