One thing I'd point out is that - at least with neos I've encountered - the satisfaction is not dependent on how thankful families are. Perhaps that's my own cynicism creeping in, but I think most people, at least once they've encountered enough angry patients or angry family members anywhere in the hospital, begin to limit just how much job satisfaction they derive from "grateful" patients or parents.
So what goes on for neo's that still makes it wonderfully satisfying? I think there are a number of things. Perhaps most importantly, I think that it's rare for someone to go into neonatology without having thought long and hard about the decision. Thus you end up with individuals who really want to be there, and have had enough experience through residency to make that decision. Lots of people don't do NICU because they don't like the ICU setting, because they don't like the fact that the patients do die in the NICU. Others choose against neonatology because they like getting to know their patients and families over the course of years/decades. There are those of us out there who love the ICU acuity of the NICU but who wish the feeder/growers would just hurry up and eat already. Many people can't give up treating bigger kids and adolescents for nothing but babies. And there are plenty of people who really like the NICU but don't want to spend another three years working exceptionally hard, watching their student loans continue to swell, and put off making "real" salaries while in fellowship.
When someone has gone through all those reasons and is able to say, "yep, the NICU is the place for me", then neos are way ahead of the game in terms of being satisfied. It's a self selection process that works extremely well.