If you're looking to obtain a specific license, I can see why you're worried about subject specialization. I'm actually a Music teacher, so I was also worried about finding relevancy to my particular field. There is a lot of freedom within the program so you can take almost anything you want and there are classes that pertain to specific subject areas. You can also easily take a course at GSAS if you want any advanced English classes. The beautiful thing about the program is that it allowed me to really examine my role as a music teacher in relation to education as a whole. I was able to build my own connections to music education in each of my classes. While I can't say that my degree has made me a better music teacher, it has made me a more reflective educator for sure. I just felt that I had already done four years in a music education program-- I wanted to see the bigger picture.
However, if you're looking to use this degree as a way to gain professional status, check with your district and make sure they'll accept the degree!!!
I did my undergraduate degree at NYU and while I'm not that familiar with Steinhardt's Masters programs, I can safely say that it's a fantastic school full of brilliant people.
As far as admissions statistics go, I've never seen it broken down by program, but I do know that the acceptance rate for Ed.M.s is relatively high at Harvard... Maybe close to 50%