I suppose one can lighten or darken anything, but most natural scenes have to be taken as they are and your only option is a split filter. My guess is exposing for the light on the sand may have underexposed the clouds a bit, but then maybe not. Only Josh knows for sure. No matter, I like it. The understated ripples in the sand take the eye up to the peaks and through the clouds, where the interspersed blue is a nice counterpoint colour to the red sand.
JMR