Maybe. Maybe not.
And before I go on, in the interest of full disclosure, I must admit that I have a love-hate relationship with advanced degrees. I’ve loved some of my advanced classes and hated others. And I remember one time when the instructor went around the first day of class asking us what we wanted out of the class (I can’t even remember what the class was for!) and my answer was that I wanted it to be the absolute last class I’d ever take in my life. Because I was sick and tired of taking classes. And of advanced degrees.
So, with that out of the way, the answer to your question depends….
If you want that MFA only in order to become a better writer, then consider how good you already are before gearing up for that degree.
It can do wonders if your writing skills are less than those of most people because part of the beauty of an MFA is that it (supposedly) lifts the student into the somewhat exclusive domain of the upper middle class and beyond, at least as far as speaking and writing are concerned and that’s what you want. So it could work.
On the other hand, it’s unlikely to help much if you already have writing skills that are equal to or better than those of your average person because you are already where it will get you as far as writing is concerned.
So think hard before you go for that long, intense, expensive degree and make sure that it will really lift you from mediocre to excellent.
And here’s another thought….
If you truly believe you are mediocre but don’t want to go through all that hassle and expense, you might consider other options that can achieve the same result. Such as volunteering in a place where educated people are already volunteering so as to watch and learn from them. Or something else — anything else — that will put you in a milieu in which you will absorb the things in an unstructured way that an MFA teaches through structured lessons.