This quest allows you to use the coins to buy things at the HV WH keeper; he doesn't just take the coins and give you a reward. To see a list of the things you can do with the coins (which includes advancing your membership level) look near the bottom of this page at Stratics. (http://lineage2.stratics.com/content/library/quests/quest.php?id=336)
You can also sell the coins to private players using your sell shop. Silver Unicorns should bring between 2k and 3k each, depending on your server.
Thanks for the reply. How do i change my silver unicorns into a silver dryade?
You need to have level two membership to trade for silver dryads. You will need 20 of each type of basic coin to do that.
To get 1 silver dryad, you need to trade 5 silver fairys and 5 silver golems at Ralford in the Ivory Tower.
Both Lorain (near Cruma Tower) and Haggert (WH keeper in Oren) will trade 10 silver unicorns for 1 silver golem.
Magister Page (Wizard training hall, HV) will trade 10 silver unicorns for one silver fairy.
Only trade the coins if you are going to use them. The coins sell much better in their basic form.