A An MBA is important if you can apply what you've learned. That's how to water the grass. I mean having an MBA is not a quick guarantee for promotion unless you're under a corporate scholarship where you can receive at least one rank higher in the hierarchy upon graduation.
Performance is always the bottom line. With or without an MBA, every corporate worker is judged by his/her tangible accomplishment.

Before you decide on pushing your luck, consider the principle "the harder you push, the harder the system pushes back." It's a classic from Peter Senge of "The Fifth Discipline" fame. You can understand this by correlating it (as suggested by Mr. Senge) with George Orwell's Animal Farm.

"The horse Boxer always had the same answer to any difficulty: "I will work harder," he said. At first, his well-intentioned diligence inspired everyone, but gradually, his hard work began to backfire in subtle ways. The harder he worked, the more work there was to do. What he didn't know was that the pigs who managed the farm were actually manipulating them all for their own profit."

Boxer's diligence actually helped keep the other animals from seeing what the pigs were doing. Systems thinking has a name for this phenomenon: "Compensating feedback." It is when well-intentioned interventions call forth responses from the system that offset the benefits of the intervention. We all know what it feels like to be facing compensating feedback--the harder you push, the harder the system pushes back; the more effort you expend trying to improve matters, the more effort seems to be required. Consider this before you tackle the rigors of getting an MBA.