I suppose I should explain why I use two different spellings for faerie. To me, they're two different things. 'Fairy' describes a Disneyish magical being, quite small, that is pretty and happy and beaming with light. They dance and fly and are really only useful as window dressing in stories I tell my daughter.
'Faerie' describes a being of ancient myth and eldritch magic. They are not happy all the time. They can be rather spiteful. They have no problem playing tricks on mortals that end up Very Badly for said mortals. I also refer to them as 'The Fae' when discussing them in general. This is intentionally done in order to make them sound a bit spookier. By giving them free will and potentially malevolent natures, they become much more interesting as story devices.
So that's why the two spellings. Maybe some day I'll also describe why I think gray and grey are two different colors.