It would be very useful to have some sort of collision control. A "strength" or a percentage control that allows you to vary the distance set by then bounding boxes.
As it is now, it is almost impossible to cover an area with grass without using an incredible large amount of collided objects. Using collision will reduce the number dramatically, but will always leave some empty spaces around every object - due to the bounding box. By reducing the collision "strength" it would be possible to make objects come closer only slightly overlapping, and thereby cover an area with less objects than now.
Regards.