I know that this is probably not a fair comparison, but I think that interest in Elder Sign Amulet will probably decline now that the Key of Ys exists. They both take up the accessory slot, are both neutral, have the same skill icons, have the same horror soak, and have the same Item and Relic keywords, However, for 1 resource and 2 experience more the Key of Ys gives you a really powerful effect. It's really hard to justify spend 3 experience on this when you can get the Key for 2 more experience because it's almost always worth it.
The advantages Elder Sign Amulet has over Key of Ys:
- Key of Ys is unique, so only one can be out at a time per group.
- Key of Ys discards cards when it leaves play whereas Elder Sign Amulet does not.
- Key of Ys costs 2 more experience than Elder Sign Amulet and experience is a precious commidity in this game.
- Key of Ys costs 1 more resource which could make it slightly harder to play then Elder Sign Amulet for some investigators.
Key of Ys is so similar to Elder Sign Amulet that if you asserted that the Key of Ys was originally slated to just be the level 5 version of Elder Sign Amulet, I would have been inclined to believe you. Of course, saying that this card is a worse version of what many would argue is the best card of the game isn't really an insult. This is a relatively well-balanced card and I think a lot of people considered it as a reasonable source of horror soak in the core set. However, I think that going forward it will be hard for people to take this card without thinking "maybe I should save up for the Key of Ys instead..."