I had a CAO Vanilla in my humidor for about 4 years and didn't notice a difference. But keep these things in mind: A) It was still in cello, B) The other cigars in my humi for that duration were not top dollar smokes, and C) A little vanilla may have just made the others seem "creamier" to me, but I had never smoked them before. But really, I never tasted vanilla in any of them.
Edit: Oh and D) I'm pretty much a newb