I have similar clinical interests. I think genetics/genomics is a great field for you, for the reasons you listed. However, it's not going to help you make money or get recognition any more than getting your PhD in some other area. In general, peds doesn't pay very well, particularly the specialties you listed, and particularly if you're doing research. You're right that genetics underlies many other fields, but I don't think it's necessarily fair to say that it would serve you "better", just differently. You could definitely do your PhD in cancer biology, neuroscience, etc. and they would serve you well too.
I didn't really realize this until I started the MSTP, but the "focus" of your PhD (i.e. cancer biology, neuroscience, genetics) is not very important. The main importance to picking a grad program focus is the coursework that you will take--once you get past the courses, you can usually pick almost any lab available at the university. My advice is to pick the grad program that has interests as similar to yours and as little coursework requirements as possible, because most grad school courses are essentially worthless.