man, get away with what you can in 2d. Meaning that you don't really need something like sss for a leaf, Just get a picture of a leaf, and tweak out the color of it until it looks right in your scene. There's a ton of pictures of leaves out there, look on flickr, or just on google, you'll most likely find what you're looking for. I'm thinking that a decent photo mapped onto a plane like tyson was talking about is going to turn out a hell of a lot better than trying to make it complicated. So in other words, yes. Keep it simple.
-Z