'interpretation and diction of the song yet sacrificing proper phrasing, dynamics and even tone quality.'

i would think that all goes together.
my recommendations are simple and free. for six months, attend a church (regardless of your religion or lack thereof) that uses congregational, a cappella singing (church of Christ or primitive baptist) and sing HEARTILY with them.

sing all kinds of stuff along with the radio...country, gospel, ballads, etc. as loudly with good tone as you can stand.

after half a year you'll know a lot more and be more versatile.

the most i ever learned about endurance was when i played in a circus band...my Lord you NEVER stop...three shows a day...i died!!! you have to get out and do it to learn which techniques work or have to be modified for yourself.

dj