As Mary said, the amulet is way too easy to get, so it should not have so many positive features.
And as far as your specific suggestions are concerned, three of them should be excluded immediately. Farming is already very profitable and quick in means of xp. Also hunter is already one of the easiest and fastest skills. To improve the chances would make it even faster, it makes no sense whatsoever.
There are various ways to collect snape grass and it's already fast via fishing, so no to this and caskets as well. I'm refusing to support the idea of making caskets and therefore ornament kits accessible.
I wouldn't mind the higher chance of getting gems, however it would have no effect on mining or collecting gems, so it's not really needed.