Turns out they are an ingredient for one of the formulas that eventually leads to the backwings...
http://www.gaiaonline.com/forum/gaia-community-discussion/sacred-key-fact-sheet-mystery-solved/t.74772651/
http://www.gaiaonline.com/forum/gaia-community-discussion/angelic-demonic-backwings-alchemy-quest-revealed/t.75964917/
So, according to DJ Helsing in this video, the Sacred Key is an ingredient for high level formulas.
HOW ******** POINTLESS IS THAT?
Scumbag Gaia. >:[
CREATES KEYS TO GET PEOPLE INTERESTED IN ALCHEMY
KEYS CAN ONLY BE USED BY ALCHEMY MASTERS
KEYS CAN ONLY BE USED BY ALCHEMY MASTERS