How do you (easily) exclude the sky from adjustments?

davidg, you're a genius - dragging the graduated filter out from the image is something I hadn't thought of.  And thanks for reminding me about the ALT-range slider.  Thanks - you've saved many hours of my life. 

Another thing to remember is that you can use the color sampler to select colors for a range mask in two ways. First, you can simply click. Shift-click adds another color sample, the maximum is five samples. You can also drag a rectangle rather than just click however. Every color inside that rectangle will be selected that way, and again you can do this up to five times. That should make it possible to select all colors in the landscape, except the blue sky.

Thanks.  I get that I can use the adjustment brush (see my option (b) in my question).   The key part of the question is "easily".  It seems to me that LR provides us with an easy way (a couple of seconds) to select the sky when we want to adjust that (graduated filter + range mask).   But there seems to be no similarly easy way to select and adjust the non-sky parts of an image, which is the more common scenario.  Which an invert option would give us.  So, as you say, we have to use the adjustment brush, which takes minutes, rather than seconds, per image.

Or, as you again say, we have to load into Photoshop, which takes time, doesn't have simple texture and clarity adjustment and uses destructive editing.

I guess I'm just surprised that (and wondering if) there isn't an easier way to do this, given that it's presumably a problem that all landscape photographers have to deal with?