See, my understanding is the wattles really depend on the genetic background of the bird. So, unless they come from the same stock, you can't tell by wattles. As I said, our dominant almost three-year-old male has no wattles to speak of. Less than the female pic above. Amongst our younger guineas it ranges and falls closer to the 'typical' male/female lines, but I would go by sound over looks every time. But, maybe that's just me?
No, you are exactly right. Like I said in my previous post, you can not just go by wattle because it is not 100% but it does often help. Also, you will see a difference in the shapes of their body. The males will have rounder bodies and stand taller; while females have flatter back and what is called a bustle. And if you look at peepsquad's second picture, you will see the back side of the White guinea that she thinks is a female. That one has a flatter back and what looks to be a small bustle.
But like you said the only way to tell for sure is by their call.