A Sorcerer or Druid with 110+ level can use Energy Strike to solo a Spectre easily. Dwarven Ring is recomned, as it causes Drunkenness a lot (if you don't want to use it be sure to not to run in their Great Musical Bomb). Higher level Sorcerers (160+) can use Rage of the Skies to kill many at once as you can kill a Spectre by 2 hits.
Note: it is posible to hunt them in inquisitions at level 110 as sorc if you get a friend making the hands runing away and clean the hffs. if you do so try only get 1 spectre and use normal energy strike. Really good exp and big profit is possible even at low level.