I'd add cadence or finding one that helps and fit your voice is necessary as well. Knowing how to stretch certain words and which ones are important. Having a style to fall back on does wonders.
Theater is incredibly good for also learning good posture for speaking in addition to how to properly push your voice out, in some ways. The only problem is that you can sound too theatrical when speaking sometimes, though since people aren't entirely used to it, they don't mind.
Also, this is a great thread.