As a girl with the knees of a husky 12-year-old boy, including the scars and scrapes, I can totally relate to being less-than-in-love with your knees. I think a high-low starting just below the knee would be gorgeous, and a nice twist on the style. I'm personally a fan of those maxi-dresses that are in style right now, but hate the thought of "swimming" in so much fabric. To take one of those and apply the high-low look starting just below the knee would probably be marvelous as well. (Sorry. I'm sort of thinking out loud here, LOL.) One great thing about making a skirt like that would be that if you try it and it just doesn't seem to work, you can always hem it a bit shorter until you achieve the desired effect. After all that long-winded business, long story short, I say go for it!
UPDATE: Just found this pic of a longer version of the high-low/mullet skirt. I think it's pretty gosh-darn awesome!