The challenge of studying at the graduate level makes people think. Unlike undergraduate work where you were required to regurgitate expert's opinions, at the master's level you are encouraged--and in some cases compelled--to think more independently and express your thoughts and idea. A master's degree will make you more confident about your teaching ability and your general life.
Holding a master's degree in education demonstrates that you have achieved a certain level of academic competence. People--including students, peers, administrators and parents--will take you more seriously if you have the credentials to back up what you say. People who hold a master's degree in education are more likely to be considered for positions as principals, administrators and educational consultants. Those wanting to have more mobility in the educational job market are well-advised to have a master's qualification.
A quick look at the teacher salaries in America highlights the increased paycheck for teachers with a master's degree. Applications from teachers who hold a master's degree are also taken more seriously when they apply for research grants or scholarships.
When planning your master's classes and writing your thesis, take a big-picture view of structuring your work so it can be expanded if you decide to pursue doctoral studies.