SAFEA guidelines are strictly advisory and, to further complicate matters, beginning in the late 1990s, the Chinese government has been increasingly moving towards decentralization: For example, what is true today in Anhui for foreigners may very well not be true in Henan Province. Unlike any Western country, the People's Republic of China is organized far more along unitary (harmonious) lines than federal principles and while, constitutionally speaking, America's fifty states have far more individual rights than do China's 33 provincial level units, in practice, local CCP leaders have far more personal discretion than do any of their Western elected officials at the same comparable level of government. In China, might makes right.
In regard to the three to 500-yuan increase you should be earning with a master's degree, all you can really do is politely cite common practice and SAFEA advisory guidelines. However, the Chinese avoid creating new precedence because, as they see it, doing so opens the floodgates for having to yield to even more concessions at a later time and, once that precedence is set, they know they will be stuck honoring it for others. If your university does not already have a history of paying foreign teachers with master's degrees more than those with bachelor's degrees, it is unlikely they will start doing so now.
Theoretically, yes, you should (will) be paid something extra for participating in these insipid departmental, university, provincial, and national English contests (typically four per year at the university and provincial levels) but administrators never seem to know in advance exactly what that amount will be because, behind the scenes, a lot of money is changing hands whenever CCTV is involved. How those monies get disbursed in the end varies greatly between events for a variety of reasons. You could receive anywhere from 50 to 150 (or more) yuan per hour. However, the chances are great that if you ask exactly how much you will be paid, you will be told "we're not sure yet" (and that happens to be true).
Universities take these painfully boring English contests very seriously and a great deal is at stake politically for everyone involved. Consequently, foreign teachers don't really have any choice but to participate in them as their involvement gives the school a great deal of face.
I think you need to start looking for a more rewarding position come next fall, hopefully one where the university administrators value the role of their foreign teachers a great deal more than yours seemingly do.