I checked with Dave Flanigan here at KaBOOM! He works with the Project Managers and has been building playspaces for a long time. Here's what he says:
There is not any standards per se about the size of the playground in relation to the size of the area. However, here are some considerations:
There is no trend that I have seen about condensing the amount of space. More open space is always a good idea.
Are there any other experience playspace designers or builders who have other thoughts?
Just one thought on spacing equipment for schools though-- I would not try to squeeze in more equipment into any given space just because with schools, you have such a high number of kids out at any given recess that it is important to allow that room for movement...I would look at it differently with a school vs. a park.