I don't know your background and competency in appraisal, but if you can handle assignments on your own and think you can obtain work independently, and especially if you're currently getting paid peanuts, then that "leap" is less risky. Sitting here looking over a report from a national firm that sent out a low totem-pole appraiser on a 300+ mile round trip to do a $1,200 office/warehouse report just a few years ago (sad face). So you're definition of peanuts could vary depending on who you are
In my experience, the MAI in present day wouldn't have earned more for me than the annual cost to maintain those three letters. Maybe not true if you get into very specialized work, though. Does your firm take a fair cut of the already low fees, and in exchange do they help share certain expenses?