I play on Master and gimp my self. I can safely say that it depends how you use it. I'm not doing any smithing and I won't start enchanting for another 30 levels or so, that little extra kick from Destruction is worth it. Now if you don't want to use Destruction you could try using the "Weapons Branch" of Conjuration or Illusion for real time crowd control. It's really up to you.
The cloak spell sounds awesome. How do you invest your magi/health/stamina?
I went 1 magicka:1 health:1 stamina. After I got stamina to 200 I'll went 1:1 health and magicka until magicka's at 300. Then I'll go just health. I reccomend you don't do this unless you want to challenge yourself early on. And yeah it's pretty awesome. Just wait until you get a kill cam on an Elder dragon with Fire Cloak active.