The Dock only uses the 128x128 icon resources, so even if you resize the Dock so that the icons are 32x32, it's going to scale down the 128x128 icon to that size. It does not switch to the 32x32 icon resource.
Also, I just checked and, even if you're using an icon that only has the 32x32 size, it will still not appear correctly in the Dock. It will still have a slightly blurred appearance. So, unfortunately, the Dock is not able to display icons in the way that you were looking for. I don't believe that there is a way around this problem.