Hmm. To me saying that matching videos or other visual information to existing synths is a closed idea is like saying that linking one page to another page in HTML is a closed idea. I don't quite understand how you could think that so perhaps I'm just misunderstanding you.
I think, what you're describing is what many people call the metaverse or cyberspace. In many ways Photosynth has the potential to be true cyberSPACE as it was originally envisioned. You describe browsing relevant pieces of the web from inside of synths and I completely agree with you.
I view building good strong synths of places as parallel to big web companies like Google, Amazon, Yahoo, Ebay, Wikipedia, or Microsoft building a big existing source of information. Once those large collections of information exist other people can link to useful information that they find there - adding to what is already there, but there has to be something there to begin with.