I don’t have AE on this station but I have used Gimp’s “HSV nosie” on the frame I sent here.
The result is a little grainy image (that would also create a harder job for the encoder) – the imaged is still posterized well: https://img843.imageshack.us/img843/1353/mvi0911dnxhd00011162.jpg
Try to decrease the sharpness in “picture styles” to 0. This will reduce the moire and will give to the overall video more natural look (and better encoder performance – after transcoding to can try sharpen it)