I know what you mean about being disappointed in the physical layout - I was too, especially since we were looking at a Montessori school with what I found to be truly gorgeous classrooms at the same time.
I would say there is more there than meets the eye. My daughter spends much time in the art room, and has experimented with tons of art media. She's worked with markers, colored pencils, done a lot of collage with various paper punches and other cut out material, done some very interesting stuff with mat board which is almost sculptural, she's had specific lessons in water color painting, has worked with various beading, and recently begun hand modeling with clay. I've observed that the kids seem to get involved in a particular art area, and will stick with it for a while before moving on. The large amounts of art material there are very well maintained and put away, so maybe if you don't see the kids working on them, you just don't see them.
There is music happening at the school all the time - kids walk around playing guitar. They put on about 6 shows a year, and lots of people perform various musical styles and dancing. Lessons are available in various things.
Outdoors is very important. I walked down with my three year old son yesterday when I picked up my daughter and the kids welcomed him into the sand area. Some 5 - 9 year old boys created structures for him to knock down, while I went into the art room with my daughter to check out her modeling work. They were showing him the difference between the dryer and wetter sand for buiding when I got back. I love seeing the mixed ages in action there.
On the way out, we looked at a fairy village around the base of a big tree that kids had created. Spontaneous projects seem to break out all the time, with various kids coming and going and being involved in different ways.
I remember reading in one of the many Sudbury Valley books that when the school was new, they installed a big play system at great expense. The kids played on it for a few days, and more or less lost interest. They took it down. They have swings, a big slide, and the sand area, some chin up bars and a "tree house" and not a lot else for "play equipment". They have some fabulous rocks and really great trees though, and you find kids on and in them all the time.
This all seems very in keeping with the Sudbury Valley philosophy. More later, I've got to go.