http://www.d20pfsrd.com/magic-items/wondrous-items/wondrous-items/a-b/amule t-of-the-spirits/
In the text of the item it says:
"If a creature that already has the associated mystery or spirit wears the amulet, that wearer does not gain the abilities listed below; instead, the effective level of her mystery or spirit powers increases by 2. This effect does not stack with other abilities that increase the effective level of mystery or spirit powers."
My question is if it applies to Oracles as well?