Don't know much about the competitiveness, but from what I've heard the pay isn't as large as cards or gi, that's for sure. I've heard anywhere from 150 - 170$ K/yr. But in the end, if that's what you really like and enjoy, then go for it.
of course, if you go into private practice, and sit around doing endoscopy all day, you can make much much more than $220 as a GI. that sounds like it might get real boring though, i personally would prefer to stay in the academic sector....
another thing -- endocrine might take a hit in terms of paycheck, but its got a sweet lifestyle going for it.... the few endocrinologists i know all seem very happy, and lead relatively normal lives.