I don't believe your first picture is over saturated even for SS and IS.  You photographed the alpenglow on Mt. Rainier, the mountain should be that orange-pink color.  Here are a few tips, wait for clouds, even if you need to go back day after day.  Don't cut off the shoreline like you did on the left.  A horizontal composition might have been better always shoot vertical and horizontal compositions.

The Salt pan shot with the clouds:  The human eye sees the brightest part of a picture first.  The use of the split neutral density filter makes the salt pan the brightest part of the picture, it overpowers the colorful sunset.

The sand dune picture is nice but you need more depth of field.  When you have a spot of light make sure there is something in it.  Again clouds would help this picture.

Oak tree:  If you are going to silhouette the tree try to have the sun showing through the branches.  Most times it will star out.  Or wait till the sun has set, but before the sky is black, to shoot.  That will make the tree and foreground black.