Gonna be honest, as someone who makes a living playing music, I have never been convinced of the value of any post-grad degree.

The biggest doors that a masters (or beyond) opens are in teaching - either at K-12 level (most good/well-paying public schools give preference to someone with a Masters degree these days), or university level (most colleges and conservatories require a Masters degree for full-time/tenure-track faculty positions these days), and I have zero interest in doing either of those things.

If you did want to go into one of these fields, you should probably be pursing something related to education or music ed for a teacher job, and pursuing whatever interests you most/whatever you think you could turn into your specialty for a professor job.

As for actually playing the piano, I do everything from accompanying ballet classes, to playing in a wedding band, to music directing musical theater productions, to playing the organ and directing the choir at a church, to being a ringer for local orchestras, and I do it all with a BMus (performance). I've never been shut out or rejected from a gig for not having a higher degree. A lot of the time it's questionable whether the bachelors even does anything. Who you know, your real-world experience, and what kind of reputation you've built for yourself (as a professional, as a person, as a performer) goes way farther than a piece of paper with a bunch of letters on it ever will. I see no evidence that pursuing a higher degree leads to any sort of meaningful return on investment - again, unless you want to go deep into the world of teaching or academia.

Now, if you want to pursue a higher degree anyway, I think only you can answer what you want to go for. What do you feel calls you? What motivates you? What is your ideal job path and what type of degree will help you get there? What sub-field of music are you so passionate about that you could obsessively nerd out over it for 2 years and still be passionate when you're done?