Actually I don't think you use your Spell modifier on cantrips, not without using a special amulet for it.
The modifier is used on attack rolls for ray of frost, shocking grasp, firebolt, and bone chill. It's used for save dc in regards to poison spray and acid splash.
I also wanted to add if I was to replace warcaster feat, I'd probably just go for another 2 points into wisdom for another point in AC and perception checks.
It is an interesting combination. If I get a chance, I might play with a build myself and post it here. Just my two cents.
