Wharton/SAIS Joint MA/MBA Program

[greenturkeypants]

I am currently admitted to SAIS for a MA in international relations/economics (2 year program) starting next fall. I am considering applying to Wharton/Tuck/INSEAD for the dual degree MA/MBA program. The joint program would add another year to the degree and be an additional ~$70K plus opportunity costs. If I am interested in energy in the private sector, how much would the MBA improve i) my job prospects, and ii) my salary.
As BG, I have 4 years of work experience, 710 GMAT, and 3.8 GPA from a Top 50 undergrad.
Thanks!