Also, SpaceX has actually thought about the problem quite a bit and until somebody payed them they clearly said they are not going to do anything moon related.
They clearly did the same calculations. Moon is only worth it, if you actually want to go to the moon.
No one would be willing to fund anything that hasn't gone through at least one viability test on the closest short term analogous scale.
SpaceX clearly did not think that for their mars architecture needed a moon testing step. Mars concepts such as Mars Direct did not include such a step.
Unless you have extreme time pressure its much, much, much preferable to test on Earth and Mars, rather then the Moon. Earth because it's by far the cheapest, and it shares a reasonable amount with Mars, and Mars because that's where you want to go anyway.
The only advantage that the moon has is that it is closer than mars in pure distance. That advantage is eradicated when you consider the much more important DeltaV.
