from the general reputation of the schools that i've heard (on various forums, online rankings, promotional material, alumni/others that i've spoken to, etc.) it seems that Oxford has already nailed down the top spot in the EMEA regions as the best nonprofit program.
i think the thing with Oxford is that, it's still a relatively young program vs. Yale. however, i'd say globally (especially in middle east and africa), the Oxford network and brand name carries more weight than Yale, and it'll likely be easier for you to land a job in a developing country after your MBA.
the courses might not be as well designed in Oxford vs. Yale, but i think there's still a pretty strong support from the Skoll Centre. i think what you lose in the academic course work, you'll more than make up with the extra global mobility, the networking possibilities provided by the Skoll Centre, as well as the 1 year and 75k you save. especially considering the fact that if you're looking to get a job in Africa/India/East Asia, an Oxford degree will open the all the same doors as a Yale degree (maybe even a few more). and by the time you're ready to come back to the US, your experiences and accomplishments will far outweigh the brand name of your MBA.
now if you're really focused on the academia, and especially how the social aspects of it are taught in the classroom, Yale might be a better fit than Oxford. however, i still think the overall strength of the Oxford program, combined with all the factors i've mentioned above, makes it a good fit for your particular case.
(btw i'm just playing the devil's advocate here trying to sell you on the Oxford program lol, although i do believe these are pretty valid points). on a side note, i do believe it's possible to take other courses while at Oxford (you'll probably just have to contact the department and get permission from them)...just not sure how busy your schedule will be and if you can fit it in.