Any mage build should make ample use of some of the most effective passive skills in the game like Destruction and Confusion. A dual wielding mage with magic missile + confusion combo is almost invincible, specially at higher levels. It's a shame that confusion is capped at L9 but even at L6 it's a worthy choice. Destruction can be trained to L8 in FoV. Firewall is another great skill but you need to get close to enemies in order to engulf as many as possible. Regardless of skill choice, Vitality, Intelligence and Spirit are the attributes where every mage should spend more stat points. Dexterity only helps with ranged protection although a dual-wield melee set-up that relies on critical hits might also be benefited since Dexterity affects Heightened Reflex.
A 'discrete' mage can do with less points in vitality but that's not a very good idea. Using priestly skills like Hide in Shadows, Charm and summonings efficiently it is possible to survive even tough battles with low health but it's always easier with more points in Vitality.
One can skimp on Spirit though and can do so effectively, even a mage! If you can avoid skills with terrible mana cost like Healing or Thousand Strike and have points in Mana Efficiency, you will be fine. Mana regenerating jewelry and armor pieces with spirit buffs should also help. At Level-38 my mage character(naked) has only 8 points in spirit and I play @hard!
Having said all that Stat points DON'T dictate the terms of this game rather they help to ease things up when leveling. Skill points do play a much more decisive role provided you spend them wisely. But it's the strategy and maneuvering in real-time that decides whether you would fly like a Dragon or crawl like a Lovis crawler
