This is one of those Perfect Solution items. Someone comes up with a need, creates an item that solves it perfectly, Nice. Neat. No Drama.
Deletion of drama is not a good thing in my mind, and forcing characters to confront the realities of how to obtain information while being true to their convictions, if any, is far better then simply waving it away.
Lie detector machines can be bested. Truth serums can kill. Tortured people can still lie.
I would, at the very least, have this amulet do damage to the victim's sanity, even if they are innocent, so one must take care using it. The more they resist answering with the truth, the greater the stress upon their mind. Good folk would not be able to use this item without having to balance the pros and cons.
I like the idea of a magic currency, perhaps usable as alternate components that apply modifiers for spells. I remember an old Dragon magazine article which listed various alternate components for the various spells, and their impacts on them.
These fit more in line with the video-gamish approach to spells where consumer-goods exist and there are lot of casters in the world - so very High Fantasy.