so im like 90% done with the game.. and im wondering what the heck the purple orb and black feather key items could possibly be used for? i seem to have numerous of both and i know they are used for something... any ideas?
If you're 90% done with the game I wouldn't bother with the material items offered by the black feather shop; that's really something to use early on. The blue stat increasing items are probably a better buy since you can find HEAPS of the high level material items in the extra dungeons.
If you feel you are so powerful that the blue stat items will not be helpful then go ahead and stock them up and save them to be carried over into the next playthrough.