Short answer: Yes.

Long answer:

I've followed pieds for quite awhile and it definitely seems to me that, while it is heavily debated whether the amount of white in the parents affects the amount of white in the offspring, the amount of white in a pied certainly is directly correlated with its market value.

The reason seems simply to be that high-whites are more desirable -- though I and many others love pieds of all degrees of white, just about everybody wants a high (or at least medium) white one.

... I honestly don't know whether high whites are any more or less common than low whites; obviously if they're less commonly produced, they would also command a higher price. I can't say whether that's a factor, though.

The difference seems especially significant in males (perhaps because females are always in such high demand). Last year when I was very seriously seeking a male pied -- medium to high white -- it seemed the price ranges were ~$600-900 for a low-white, $800-1000 for a medium white, $900-1500 for a high-white. I reckon this year all prices will be a fair bit lower for males, particularly the low-whites.