How important is bloodline?
Lineage can and does play an important role in the development of a koi-- it's color, body conformation and patterns. For example, you just bought a 30cm koi and you hope it will become a champion someday. There are no guarantees but what tilts the scale in your favor is it's lineage--bloodline.
That is why a koi from a good bloodline is more expensive then one from an unknown or unproven bloodline.
However you should be aware that famous breeders and bloodlines can be overused and abused, and they most certainly have been here in the United States. Therefore you should always investigate before you buy.