So the official rules state each player should contribute 8 treasure tokens totaling 15 points.

How does one rate the value of unique treasure such as the Barbary Banner? What about detrimental treasure like Missionary?

Unique Treasure is valued at 0 gold.

Ah :) Vielen danke :)

but, one must ask himself, how can you put a gold value on scurvy? ;-) all i can say is "priceless", or the look on your opponents face when they find your Natives, i repeat myself "priceless" but, yes, technically, 0 gold is their worth.