For me, painting the same subject in both high-key and low key goes in to my SEAL (Self Engendered Art Lesson) bucket. I've seen them, I just don't usually do them. For those not familiar, a high-key painting is when you drop out most of the bottom half of your value range and what is left is what is on your palette. Those colors can be a lot of fun! A few darks can sneak in here and there but overall the painting will be quite light, as if all the shades on all the windows have been removed.
These are two studies, the one on the left is done in high-key. Notice how saturated some of those colors are, especially on the duck's right (shadowed) side. Which do you prefer?