This is just something I came up with yesterday after fiddling around in XSI’s hair system four a few hours trying to get the look I wanted. To be sure you can get real enough grass in XSI fairly quickly…but if you want to create a particular look it can be a slight task. I actually find using Ben Rogal’s old Bhairy plug for XSI easier to use since it has very nice jitter options etc. The only catch is that Bhairy doesn’t really do dynamics so much (though you can fake it in certain ways).
Putting aside the 3D attempts I went ahead and painted a quick test grass layer in PS to be used in AE. Really all I did was import the PSD grass file, layer and scale it back, then using a levels effect change the gray point of the files. The rest is 3D layer camera animation, and animating the translation of a CC flow motion effect on each grass layer. I threw in an older cloud render at the end to add even more movement.
It looks promising for a toon like wind effect- now I need to layer the flow motion effect so that the grass sways with the wind in one direction quickly, and rebounds more slowly.