Should I upgrade from A8L D3 to A8L D4?

Finally my sis and her husband got a 3.5 years CPO 2017 A8L D4 with 13k miles on it for $50k from Pacific Audi in Torrance, CA. The car has most of the options they wanted – Executive package, driver assistant package and in pristine condition. After driving the newer 2017 A8L, I couldn’t tell …