If other conditions are right you'd get shadows in the clouds from the gravestones if you turned on raytraced shadows in the cloud layer Quality tab.
I kind of like the simplicity of the scene as it is. It's the kind of thing a photographer would be thrilled to come across in real life, but when making a virtual scene we often think "oh it's not interesting enough". Ironically photographers often look for that more simplified look in real life. So personally I'd stick with it and work on making the moon mapping work, and yes maybe see if the "rays" (really shadows) will turn out with that option on, although it will increase render time a good deal.
- Oshyan