There seems to be quite a variation among cars in terms of how tightly the rack is held with the stock bushings, so ymmv. Some of the previous threads describe cars where the rack moved enough side to side that the steering wheel would actually change its orientation in the straight ahead position when turned full lock one way or the other, or even under quick normal turns. Mine never did that at all.
I noticed an immediate difference with the Whiteline bushings, but it wasn't huge. Primarily more precision around the center zone. But for me, definitely worth the effort.