In vanilla I never used but sold them off. You got a lot of gear with intelligence boosts and the books from the Teller of Secrets. My mage ended up with 23 intelligence. In EE the books have been limited to one set and gear is harder to find in loot so you have to choose cautiously which attribute you want to focus on. You can offset loss of perception with gear and still use the codex to boost intelligence if you don't mind not having high perception but that only helps pure spellcasters not hybrids like battlemages.
