I've been listening to a lot of Elis Regina lately (one of my favorite singers), and I am just blown away the more I learn about her work. Her voice has the power to move me to tears within 2 seconds, and her body of work is versatile and ranges from the soft and delicate to the forceful and powerful.
In keeping with the theory of the 10,000 hours, there is a certain level of mastery you have to have over your voice in order to be able to use it to maximum effect. It's been said that the best singers are always the ones who use dynamics the best. I have to agree with this.
You have to also know that your voice has the power to move people in order to use it to move people. Listening to Elis Regina, it's clear that she knew the full power of her voice; therefore, she used the full power of her voice. She knew when to back off and when to let it rip, and that's what separates her from so many singers.
Just some thoughts. If you don't have Samba Eu Canto Assim go buy it right now.