Is illusion worth for a master assasin like me?

[hershangames]

So I'm a master assassin, I completed the dark brotherhood and thieves guild's questlines and the only stealth perk I lack is the last one. I have an almost fully muffled light armor with all designed to make a perfect one hit kill.

Today I entered the mage school to become awesome at illusion and, who knows, maybe conjuration. But right now, the question I ask myself is: is really worth the time? And if it is, what spells should I use?
I understand conjuration might save your ass when you miss the hit but I'm not so sure about illusion.

Please answer as soon as you can.

 

[Corvus]

Illusion has some good spells fir stealthy characters (and the quiet casting perk).
Muffle, invisibility, frenzy(and all spells with this effect) and calm (same for this one), are very useful.