Smithing and/or enchanting cannont increase the damage of destruction spells. They can dramatically increase the damage output of weapons, however.
Umm....... you may want to look again.
Middle tree... "Skill enchantments on armor are 25% stronger." Also, "Health, Magicka, and Stamina enchantments on armor are 25% stronger."
The first boosts Destruction skill. The second gives you more magicka, thus allowing you to cast stronger spells. Neither of them is related to weapons except for the first, assuming you put it on weapon skills rather than destruction (same result, though, to all intents and purposes.) I suppose you could also argue for the second for power attacks, but that's more restricted than boosting general magicka pool, after all.
Anyway, I'm busy playing... so have fun, everyone!