you can read details of the new program on the MTNA website. i did not spend too much time reading it, since i am already certified, but from what i understand, it is more based on understanding and teaching repertoire, and communicating your knowledge to the students. the old method was more 'old-school', involving getting recommendation letters, university transcripts etc.
what you get out of the certification depends on the individual. if you are a performing concert pianist, obviously you don't need it, if you are a full time professor teaching at a recognized institution, obviously you don't need it either, if you are a private studio teacher, then i totally recommend it. for me, it made me put together a portfolio of my career, student achievements, etc and it made me think about various issues in teaching, professional development opportunities, and ways i can become a better teacher. One of the things i did under the old program was to launch my own studio website - and yes i have gotten many new students since then, so there you go, at least one specific benefit!
Topic: MTNA Certification