I have 18 S&W 3rd generation pistols now and I'm waiting to pick up two more over the next couple of weeks. I've completely disassembled, cleaned, inspected, replaced parts where necessary, lubed and reassembled each and every one of them. All of them received a new recoil spring, most got a new grip, some got a new mainspring and a few others got a new firing pin spring.
I've only had to replace one side plate, one rear sight set screw, one or two small ejector springs, a couple of grip pins, two trigger pins, and a couple of slide stop plunger springs, one was weak and the other was the wrong spring (yes the factory does install the wrong spring on occasion).
The most challenging replacements were three trigger play springs (1990 4516-1, 1990 4566, and a 1992 3913). My brother cracked and broke the trigger play springs in the two 45's that he previously owned. His method of zealous cleaning was a bit much for them.
The 3913 was carried by an LAPD sergeant for a few years and was also subjected to some vigorous cleaning.
Speaking of my brother (whom I love very much), the side plate on my 4566 was replaced because he had severely bent its fingers that grip the groove of the sear pin. I think it happened when he was exchanging the straight grip for a curved one. It happens, no big deal.
So, as you can see, except for the recoil spring, maybe the firing pin spring and mainspring, there's not much to do. A new grip is mostly a personal choice based on appearance. I find a new grip will usually make a 95-96% 3rd generation pistol look like a 99% firearm, and they're only about $15 each with the C&R license discount from Brownell's.
A word about recoil spring guides. S&W makes a solid stainless steel recoil spring guide for the 4006, they call it a CHP recoil spring guide. It also fits the 5903, 5906, etc. I have use one of those wherever I can, but that was a personal choice and not "required." The same goes for the solid stainless steel recoil spring guide they make that fits the 4566, 4576, 1066, 1076, etc. Those, too, were my personal choice and not required.
I addressed magazine springs and extractor springs in my previous post in this thread.
FWIW and HTH