yes is worth but only if cut out by hand = clean
Yes, if you cut them clean with 200% zoom on your outlines, they do sell. However, the time that takes and patience to do that - you can upload lots of other images and make the same or more money on them.
Contributors who do best selling png work are excellent at it: shadows, grass, fur, hair, dust, raindrops, explosions, elaborate food, etc. if you will learn how png behave on various different backgrounds, they will sell. If you cut them automatically and they will end up with a halo against white or black background, they do not sell.
I know some designers who are wicked fast at clean png. I never got that fast, even my first png was 30 years ago.