Yes I really enjoyed the stone money on Yap. The difficult part is to get there. Today (Jan. 2020) just 2 flights a week go from Guam. The flight from Palau isn't scheduled anymore. I visited already 2 years ago but finally have time to edit some photos and write my review. 

This money is everywhere on Yap. You'll see it at all the Faluw (Men's Houses or meeting houses). Even if you walk through the bush you can come across it. Some roads have it lined up on the side as well. It's protected each single stone how small it can be from 3 centimeters up to 4 to 8 meters wide. Most came from Palau where you can see the quarries. The bigger the stone, the nicer the stone and the more you have/had the wealthier you were. Interesting to see this legal tender. 

Yap is a small island and all places of interest can be seen in a day. As flights are twice a week you're always stuck there for 3 or 4 days. Snorkeling and diving is highly recommended.

Worth a WHS? For sure yes and I hope with the quarries on Palau together. 

(photo is copyright by CTB Global, can be used on Worldheritagesite.org but not on other sites)