With regard to reading back only the numbers and leaving out the rest of it, I once heard an exchange something like the following (details changed to protect the guilty) :-
"xxxx 321, turn left heading 120 degrees, speed 180 knots, descend flight level 130 and contact Director on 123.45"
"12018013012345321 - what a load of b******s!"
Sorry, for me it doesn't add to the clarity or (therefore) safety.