There is also the possibility of finding shore duty near a good business school, and earning the MBA during the last tour before you get out.
That was pretty much my approach, althought had intended to remain Navy for couple years after but .....
I think would depend somewhat on your MBA career track. In the final analysis, it depends on how much you learn, coupled with networking opportunites that an "On Campus" environment provides. Agree you should not ignore "on-line" studies. For the entry level jobs the MBA is invaluable. As you go up into the six figure positions, the MBA counts as a "punch on your ticket" but not as essential as someone without any "real world" experience.
I finished, well almost, at the Kogod School of Business - American University, WashDC, during my shore duty tour. Interdisciplinary MBA, I was technical - Computer Science. Focued on security of computer based accounting systems in large enterprises. Completed all but the last Seminar and Comprehensive exams prior to end of shore tour. Requested six month extension to finish, Mother Navy said - We need you at sea, you can finish by USAFI correspondence course. Think the Navy is more civilized these days, but that is a "guess". (Letter, signed by BuPers hangs on my wall)
It was tough completing in three years, carried a full load of courses along with the day job, but thankfully my only other duty was bi-monthly CDO watch, which I spend most of the time studying!

Was also across the street from American U, current Homeland Security HQs in NW DC which made life easier.
Left the Navy to finsh, was in very "high demand" both from the perspective of American U connections as well as an emerging field (computer were new then

). Continued on in a Phd program, Professional Degreee in Research and Development. Turned out the University could not get a professional degree approved, they opted for an academic degree. Decided that it would amount to truely "Piled Higher and Deeper" ticket punch, so decided not to continue. Right decision, in retrospect.
Guess my message is look around see what is available and make the most of each opportunity to presents itself, but by all means go for it.
Check out Kogod - they have a chat room to discuss our program.
www.american.edu. Even though you do not intend to go there, they can give you some more information - short of TMI.