MAPSS alum here. Started with an interest in political theory but shifted to another subfield after taking some courses. I will offer my two cents.
-The political theory job market, and as a consequence, PhD admissions in political theory, is dwindling and becoming increasingly competitive. If you are unable to go to a top top school in PT, your job prospects look increasingly grim by the year. I am certain the Trump administration won't help this. Keep this in mind.
-Whether you are set on PT or another subfield, MAPSS can be valuable under a narrow set of circumstances. These are:
1) You are dead certain you want to do a PhD in a social science and do not think you will be able to get into a top program without doing MAPSS.
2) If (1) is true, you need to hit the ground running and gear your MAPSS experience to securing a PhD admission at a top program after completing your MA year. This means making strong connections with full time, tenure track faculty, performing exceptionally well in their classes (speaking in class, writing good papers, etc), going to the workshop in your subfield (there is a PT workshop at UChicago) and, above all else, writing a great thesis supervised by a full time, tenure track faculty member. If you are in a subfield other than PT, you definitely need methods training, and should try to do quant and qual if you can.
3) If (1) and (2) are true, you need to be able to afford whatever MAPSS and living in Chicago for a year can cost you without it ruining your financial life.
1, 2, and 3 were true for me, and I have managed to turn it into being admitted to a top 15 program. If this had not happened, it would've been a colossal waste of money. Having a MAPSS degree did not help my job prospects at all upon graduation, and I ended up in an entry level job that I could've gotten straight out of college.
Best of luck making your decision. PM me if you want to talk more in detail.