Just because a piece is old, does not necessarily mean it is more valuable. Catalogs can give you a feel for this, but nothing substitutes for becoming familiar with the real pieces. In New Guinea villages, masks and other items are stored in the rafters between ceremonies. The paint wears off or is covered with smoke from cooking and mosquito fires. Before a ceremony, the carvings are taken down, cleaned and repainted, decorated with feathers, flowers, ornamental fruits and colorful leaves such as crouton.
Ceremonies are very lively and the costumes bright.
Another reason for this is the agricultural and environmental restrictions on importation of feathers and other products. Beautiful feathers are quite valuable in New Guinea. They are removed from the masks between dances, wrapped carefully and stored. It is unusual to find anything other than chicken or the common cassowary feathers on a mask that is being offered for sale. There are restrictions on what may be legally exported.