I just rechecked your industrial pics, very nice! Can't believe I missed a few posts.

Yeah, that thought did cross my mind while I was taking the pictures. Japan isn't quite as paranoid as some other places but I figure as long as you are in public areas and honest about what you are doing you shouldn't have any problems. Of course, "shouldn't" and "won't" are two different things.
The area I was photographing in actually has tours (during the daytime) and is even a somewhat popular destination for industrial photography; I saw two other people taking pictures that night.