What about Polarizing filter?
That is do the job and not need manipulate the picture.
Actually it make even better result, then just rising contrast in PS.
But yes, of corse in that case the clouds must be there when a picture is taken.
On a #1 picture left upper corner on the sky you can see a wierd effect on the clouds edges. They are repeating themselfs, which can happen if you overlay the same photo, but slip off a little. But because this isn't happen any other places on a picture it is shows that portion of the picture was moved separately, waht indicate that, this picture was put together from more then two shot, or it was extensively manipulated, even separated the sky and some part of it was moved alone.
May be just a color was canged sepapartely on the sky, but when it was put together again some portion of it wasn't align carefully.
You can avoid this kind of mistakes if just take a good photograph and eliminate the post processing, manipulating part of it.
