So, a basic gallery is working on the WP test site
http://test.randomland.net/wp/galleries/ . I edited the media-tag templates so things look 10% nicer. Still not a finished product, but useable.
All this is well and good, but I have found that wordpress does not support synonyms in their taxonomies (they hardly support taxonomies at all, really) and this is a point of annoyance for me. So a picture tagged tree and one tagged trees will create separate gallery sections rather then appearing as one.
This won't be a problem if people are careful tagging things, but could lead to some frustration and maintenance in the future.
Grrrr. Does no one share our vision!