There's one consideration to new vs. old that continues to resonate with me. If I have a pre-IL model that is somewhat low production or desirable for whatever reason, it cannot be replaced with an identical model should it become damaged. I realize such reasoning could result in never shooting/carrying an older model for fear of hurting it, but it still nags at me on occasion. I've owned a few S&W oddballs (396, 242, 520) and I've used them sparingly simply because it would be near impossible to replace them. With a newer S&W, irrespective of MIM or IL, the Mothership will generally replace it no questions asked.
Aside from some cosmetic elements, and speaking strictly as to functionality, a new S&W revolver is a fine purchase.