For the last part:
A flawless brier pipe is so valuable to collectors because it finding one is exceptional. It is extremely rare and it does not grow anywhere. This grows mainly only on the rugged coast of the Mediterranean sea. It is not easy to make a brier pipe, it will take many years. Moreover the process of making a fine pipe is long and exacting. It means that it can be very expensive. The production of an excellent one is unique. At least just three out of a thousand get an excellent grade. Because of this the collectors have treasured these find.