Enchanting has never been useful for my mages. Really, Enchanting seemed like a warrior thing. Of course, I've never played a mage without Illusion. On master level. Don't know how that'll work. 100 health and 100 stamina, wearing robes and no armor...WITHOUT illusion. But it's something to try. Could be fun.
I felt this way too, until my mage fairly high level and I saw that the higher level destruction spells cost an insane amount of magicka. Most of the master spells in this game you cannot even cast without enchanted spell cost reduction gear, no matter how many points you put into magicka and spell cost reduction perks. So, I have now come to believe that enchanting is essential for a mage and you can trade the 8 points of enchant for 8 points of spell cost reduction in two schools and be even points wise.
Of course, the mana inneficiency at high level problem is worse for destuction, where you need to repeatedly cast spells during combat, than it is for other schools, like conjuration, where you cast a master level spell once outside of combat and then have your thralls follow you into combat. So, if you had a mage that focused more on conjuration or illusion, you might not need enchanting as much. But for a destruction mage it is pretty much essential, unless you want to impact stagger with a low level spell all day. But that gets boring fast.