To bring out definition in clouds, initially a polarized filter would be highly recommended while shooting, especially a scene like this.
As Puckman said, you can use the GF in LR or the Brush as well. However my point is use a polarizer, and you will be doing a lot less editing in LR and get better results, and then tweak as needed in LR
In my edit above, I used neither the GF or Brush in LR, just some adjustments in the Basic and Tone Curve panels.. With the techniques I use, I could of brought out definition in the clouds, however I didn't touch them
If you look at nittaya's sky edit, with the attempt of bringing out definition, color noise was added in red & green shades. That could of been remedied in LR
I think Spikes edit is more in line with your taste and perhaps his, as it appears he left water and sky un touched and added contrast to the tree line on both sides of lake.