Yes aoe skills are worth leveling. You get more out of snowstorm than you do hellfire. The bard's Hellfire is great and you can heal while keep a constant stack of the skill on enemies. Aoe for mages work better when you have a party or a tanker to take on damage or keep provoke/aggro. Unless you have pots to keep your HP up enough to completely wipe out your targets.
Lightning, along with Fire Bomb, should be up-to-date in level. You want the most out of your single attack skills since you rely on those constantly while versing enemies. Most people either use Fire/Lightning or Ice/Lightning n stack Ice..(i think you can stack it).. Lightning is a insta shot skill so you can immediately use your next skill without much delay.
(¸.·´ (¸.·`¤.Tea.. ¤