One of my alts, Ethne, has the Echo. It's an important part of her background - the visions are a driving force for her.
I don't see it as Mary Sueish. It can be an interesting plot device, if used well. Just make sure you ask for permission before having a vision about someone, and you're fine.
I don't see it as Mary Sueish. It can be an interesting plot device, if used well. Just make sure you ask for permission before having a vision about someone, and you're fine.