I've considered doing (another) post grad evolution, for personal fullfillment. MBA would be pretty low on the list... not particularly interesting or useful for an established pilot. Unless you want to get into flight ops management with an eye to working your way up the food change to big money jobs, MBA would be of couse applicable to that.

Consider aviation safety, safety management, or similar. That's very relevant to many union and management jobs, and would be pretty interesting to me anyway.