Looks like the nerf was around
March 2003 (Shortly after Ykesha was released)
The items that sold for around four plat were:
Aqua Goblin Backbone
Aqua Goblin Headress
Dirjadak's Chipped Stein
Vial of Aqua Goblin Blood
The earliest mention I can find of the items being worth that much looks like around August of 2002, so well after the Luclin release.