It's just my personal opinion, but I would never again allow an older model J-frame in good condition to slip through my hands. I'd keep the older one and save up for the newer one.
I let an outstanding nickel 3" heavy barrel pinned & recessed M36 slip through my hands just because I was in a hurry to get something else and another cop wanted to buy it.
I let another even older M36 slip away, too.
I'm glad I kept my older M649 Bodyguard and didn't get rid of it when I wanted a SP101. Nowadays the SP101 stays in the safe.
Granted, I'm one of those guys who thinks that owning just one J-frame isn't enough.
I presently have 5 of them and have been thinking of picking up another one or two of them to round out my 'retirement CCW' collection.
I own a pair of 642-1's, one of which I picked up when they released that special run of them made with pre-ILS frames. I happen to like the 642-1 quite a bit. I also happen to like my M&P 340 (in which I carry .38 Spl +P, although I'll mix in some Magnum loads for training & qualification from time to time).
I guess it just depends what you want, what you expect and how well you can use the little 5-shot wheelguns.
I have it in the back of my mind to eventually find a 638 rated for +P someday, made back before the ILS, but that's because I happen to like the little Bodyguard configuration and wouldn't mind adding one in an Airweight model.
One nice thing about S&W is that they offer an amazing variety of J-frames.
The M40 & M42 look pretty interesting to me, too ... as does the new 640 with the dovetailed frame for night sights front & rear.
At this rate I'll probably end up with more J-frames than .45's ...