Sometimes enthusiasm can be infectious and can motivate people. Sometimes the leader will be the one person in the room who doesn't get excited. It's good to learn both how to have a wide emotional range AND to keep yourself under control.

Age helps with self control. I improved my emotional range by taking acting lessons in the Meisner technique.

My natural voice used to be flat and emotionless. It might have had something to do with my family life or with how I adapted to getting picked on in elementary school.

I've learned to put more range in my voice and I think it helps everywhere from work to flirting (I can't say dating since I'm a family man.) I used to be terrified of job interviews and now I'm not. It's opened up a whole new world for me.