Often parks within the city carry a fairly large initial construction budget. However, over time they wear down and are in need of repair. Most cities have revolving update budgets that handle "face lifts" for parks to help keep they to an acceptable level.
A new concept is to have pop up temporary parks. Boston, MA had a very successful version of this with
Lawn on D. The park has provided a venue for almost constant performances and events throughout the summer. At one point, the glow in the dark swings were the number one tweeted image in the world.
My apologizes for the terrible picture.