I use to think that too and I have heard people say they are a dime a dozen, but I have had relatives and friends who got one and the MBA really helped them. Not all MBA's are created equal and I think it depends what you do with it.
One of my relatives got an MBA from a top business school and did an internship overseas in Germany learning international business. The MBA was very expensive but he claimed worth every penny to him. He touted how great the MBA was and encouraged me to get one. He said it taught him how to open his own business and make a lot of money on his own. He now has two houses and makes like 400k+ a year working out of his home running his own business. He swears by the MBA and said it was the best investment he ever made. Now he always was a very talented individual that was considered a gifted student and was labeled a brain. I never pursued the MBA because there is no way I could get the GMAT score did, he scored like in the IVY league range on his GMAT.
I know other people who got MBA's from much less prestigous schools and it seemed to have helped them a lot. I knew one older gentlemen who origionally got his bachelors in Education and tried to be a school teacher, but couldn't manage a classroom and got fired as a teacher. He went back to school and got an MBA from a non ranked school that wasn't that hard to get into. He went on to making a 6 figure salary the rest of his life working in the business sector.
I know another relative who got an MBA from the University of Phoenix for a very cheap price compared to other schools. The MBA enabled her to move into HR. She had her undegrad in like psychology. She now works as an HR manager making 100k+ a year.
On the other hand I also know a guy who got an MBA from a top business school and he works as a truck driver. He used the MBA to work in finance for many years...but after he found out he could work as a truck driver making the same salary or more than he did working in finance... he choose truck driving instead. He said truck driving was much less stress and a much easier job for the same pay. He makes over 6 figures doing over the road truck driving and loves it.