I suggest that you visit and read up on the MD/MBA sub forum of SDN.
It is largely a deserted and stale place, but there is a wealth of valuable information rendered in threads of yore -- despite the lack of active discussion.
Individuals that hold the MD/MBA combo are in no way aligned to make more or less than their MD-only counterparts; however, due to the extreme costs involved, for most it is a bad financial choice to pursue the standard 5-yr MD/MBA joint degree.