Yep - dual wielding with +magic damage is the only way to go for a caster. And Magic Missile is particularly effective because each missile gets the bonus, so you get up to 7* your +magic damage bonus per cast (level 15 MM = 7 missiles per cast).
But dual wielding is also very effective for a melee character, as the enchants 'cross charge' (affect both weapons), so you're getting double the value from each +damage enchant. Use 4 malachite gems (+100 magic and +100 physical on each weapon) and you've boosted your per-attack damage by 800 points. I'm not sure if off-hand penalties or bonuses (from dual wield skill) affect the +damage bonuses though, but I suspect they do from what I've seen, in which case you can get more than double the value from each enchant.
Other items with +damage enchants (e.g. amulets) will also 'double up' when dual-wielding, but you can only find them with built-in buffs, as you can only cast your own +damage enchants on weapons.
@Cinco - I've been praising the benefits of dual-wield in DKS for ages on these forums, so it definitely 'doubles up' in DKS.
