This has been an issue I've had with DCA since the beginning. Lack of trees and other plants on top of very wide, concrete/asphalt walkways give the park a very barren feeling.
Disneyland, by contrast has narrow pathways (actually fairly wide but broken up by planters into more meandering paths) and much more greenery (trees, shrubs and flowers). This all works together in making Disneyland feel more intimate and block out views of other areas of the park, outside world. If they can do it for DAK then they can do it for DCA. I'm really glad to see that plants were added in front of the SF row houses recently and that the plans for BVS will include a LOT more trees and plants.