Hi Dave,
Sorry I haven’t been able to be more active in your project this fall. I’ve followed it and planned to join in but then a student stays after school for one thing or another and another day is gone. The more one does, the more busy one gets.. what else is new? A few thoughts:
Before more people come to the site and add more content there is another relationship between the new photo content and the original content. If the photo has a tag and an original tag has a piece of content, once you linked the photo to a piece of content the two tags also have a relationship through the shared content.

There is some relationship between the new content and the new tags relative in space to the old tags and content – is the placement random?

When you talk about the new knowledge coming in, isn’t this the essence of the power of database design?

Have you followed the development over the years of thebrain.com? I believe it was started in about 1993/94. There was also a very interesting visual chat that was being developed at MIT around the same years. It had a series of colored dots of varying sizes. I wonder what came of that. I always found it fascinating.