Have you found the knowledge in MBA programs as a useful asset for your professional life?

Yes it is, as an engineer myself and working in IT MBA have expanded my are of knowledge to financials, human resource, marketing, etc...
This will be useful in the future specially if you are going to open your own start-up or hold an executive position.
The only downside from my point of view is that MBA studies give more emphasis on large corporation case studies and practices and not small business environment.

Yes

Yes it is. Not only MBA but having a Masters Degree for that matter. Education (likewise continuing education) is the only wealth that no one can take it away from you. Having it at an advance stage is a plus factor. It is personal development. It is what professional people and educators are looking for. Be proud of having it!

I think so yes, MBA enables you to become a confident person (in general), to lose your fear of public speaking, to learn how to write business reports well, crunch numbers, do market research, perform qualitative and quantitative analyses, and use the results of the analyses to make decisions that lead to efficient work processes.....

It's totally depend upon your interest.

Yes