Energy determines how much mana a character has. ;
Dexterity increases your Attack Rating ;
Vitality increases your life pool.
Spell damage is always successful, leaving the melee (strenght based damage) and range damage (dexterity based damage) rely on attack ratting for their success rates. Making things, at least on a probable level quite balanced.
So no, there is no way to increase your spell's damage, unless you find items with skill bonuses (+all skill levels, +class skill levels or +individual skill level) or elemental damage increasing stats, like x% to lightning, cold, fire and poison damage.
Haven played D2 in a while now, but I don't think I missed anything.
So yeah, mage like characters/builds always hit their target, and str/dex characters rely on attack ratting, and low attack ratting equals less potent when it comes to deal damage.
Gorok just forgot to mention that Dexterity also increases your chance to block when equipping a shield which is capped at 75%
But yeah, in general, the +1 to all skills attribute on items is used to icnrease spell damage. Also, with LOD they introduced the rainbow facets and other items that increase the damage output of a cerain element and decrease the monster's resistance to said element.