anybody got any idea how much vanilla TV adds to its Rock Candy Syrup?

havent had it by itself, so i cant judge, but the website states it has a "sweet hint of vanilla."

all this time, i've just been making 2 parts sugar to 1 part water.

I'd just use an eyedropper, and add a couple of drops at a time, until you detect a "sweet hint of vanilla." You don't want to go much beyond that, or you'll start crossing into "weak vanilla syrup" territory.