MBA's are somewhat general, but there's still a lot of value in the right program. The problem with “the right program” is that your options are somewhat limited. My attitude is a bit snobbish around MBA's, but anything less than top 20 wouldn't be worth my time, and anything less than top 10 wouldn't be worth my money.
I'm sure within quite a few companies, any MBA can be used as stepping stone towards a promotion – perhaps from low-level management to middle-management. However, in looking at the money and time investment – especially if this is a long-term play towards getting into a “prestigious” or name-conscious field/company – I'd strongly recommend either going big or focusing upon a specialty and not doing the MBA path.
For many people, an MBA is a reset button, and given that you only get to push it once, I'd strongly urge you consider what you want to accomplish with it. If the intent is to move into industry, an online MBA could work – but I wouldn't bank on it being a ticket into corporate development or any strategic role. If the intent is to move into consulting or financial advisory, then don't even consider an online degree. It won't be considered good enough. No partner pitching a $2mm+ project is going to want to let the prospect know that someone with a “Phoenix online MBA” is being staffed on the project. If the intent is to get into PE, IB, or equity research, then completely erase any thought of online MBA from your mind. If you want to broaden your knowledge, Udacity or any of the other MOOCs are a much more cost effective option than an online MBA. Frankly, as someone who's interviewed hundreds of people (a handful of which were MBAs), I can tell you that I'd have 10x the respect for someone who took Udacity's entire course catalog than someone who got an online MBA. At least then I'd have some confidence in their ability to understand cost/benefit analysis and relative value.