It still has some value, but Bliz made Essence of water much eazer to get, and i have noted a decreace in the essene of undeath i see in Strath runs.
For a long time EoU cost 3 gold and EoW was at about 11 gold, essence transumtes are on a 24 hr cooldown unlike arcnite. So there was a large chunk of time where an alt could log on every 24 hrs and make 7 gold(AH fees and the like). I guess that bliz has worked to normalise the rarity of EoU, and there fore reducing the value of your trasmute. 350G is outragous, honestly 30-50 gold is fair, but most posters dont want fair, they want to be loaded!!!!