I went through MAPSS, and there are some caveats to keep in mind:
1. The quarter system at UC is brisk. If you do not possess the kind of personality that makes the room shine when you walk in, or gregarious enough to force the room to shine, rethink attending MAPSS. You'll have a very small window in which to make an impression with professors, and that is the primary consideration for getting one's money's worth out of the MAPSS program.
2. When I attended, students had to scramble to find thesis advisors. MAPSS students are not always the most welcomed by some professors so if you have someone specifically you'd like to work with, better attempt to develop a relationship with him/her BEFORE you arrive on campus (or even accept the program).
3. Stellar academic backgrounds seem to help open doors but then again, do such backgrounds need a boost from MAPSS? Fair to middlin' apps (relative to the accepted cohort) will struggle unless, as I said at No. 1, you have the knack for impressing professors... quickly.
4. Tuition assistance or otherwise, all applicants must SERIOUSLY consider the costs incurred. This isn't a cheap program by any stretch of the imagination.
5. MAPSS is best suited to help those who have a very definite direction, that direction (or interest in that direction) can be found within the UC faculty, possess the ability to quickly win over a UC professor, but are coming out of a weaker undergraduate institution and really need a CV boost for a PhD program. Even then, seriously consider the costs that will be incurred, versus one's long-term prospects in the academic job market for social sciences, which isn't great at the moment.
6. Yes, if one is planning to apply to PhD programs after MAPSS, plan on waiting out the year after MAPSS, because no one will help you pull together your grad school app until after you have finished the program.
All that said, MAPSS does provide access to a number of great professors and courses that otherwise would be inaccessible.