I'm not an ID specialist, but my understanding is that most who do ID will practice at an academic center; there will also be some sort of research expectation like there is for anyone at such a center. There are a few private practice ID people, but they generally do a lot of gen peds as well. The pay for ID is definitely at the lower end of the scale, often less than what general pediatricians make. I don't know what the current job market is like, but can ask around.
Despite these down sides (?), most people I know who do ID love it, and are very good at it. There's a huge amount of diversity in it, so it's easy to find something that can interest you, from tropical medicine, to infection control and epidemiology to specific bugs or viruses. One of my friends is a world expert on Staph aureus, and gets really excited whenever he gets to geek out about all the different virulence and resistance mechanisms it has.