Yes, I used the old wires to pull the new ones through the wall. You do need to take much care with pulling, if the wire gets stuck, try again, don't force it. I tried pulling hard and broke the old wires first time, I got lucky because there was still some left exposed.
I don't know how much influence it actually has, but I did not feel comfortable with those thin wires driving the speakers. Some say thicker wire makes a difference, other day it's nonsense.