Is it still unnecessary if someone wanted to pursue a career in corporate, business, or securities law?
Yes. It is still unnecessary. If you want to pursue corporate, business, or securities law, 1) take relevant classes in corporate, business, or securities law, 2) get involved with activities at the law school related to corporate, business, or securities law, and 3) seek practical experience in internships where you will learn more and have exposure to corporate, business, or securities law.
An MBA is a flexible professional degree is you want to start your own business, go into market research/brand development, I-Banking, etc.
Sweeping generalization: A lawyer with an MBA is simply someone who hasn't decided what he wants to be when he grows up, so he's going to flit from professional degree to professional degree in the name of "flexibility." Law firms have looked negatively at MBA's, thinking that you are not going to be a long-term investment.
Let me put it another way, would it be better to do the joint degree, or do them separately, maybe even at separate institutions? And, is the MBA a valuable degree after you have a law degree, or is it useless?
An MBA is useless unless it comes from one of the top MBA programs. An MBA is useless unless you have some real-world life and work experience coming into the MBA (even if it is not business-related).
I don't see where a lawyer would benefit from an MBA unless he is starting a firm and hasn't developed the common sense to figure out what he needs to do to incorporate it as a business or develop a business plan. And even then, you could learn those things on the job or by hiring an accountant.
the MBA is great if you know what you want to do with it. But tacking on multiple degrees for the sake of having more art to hang on the walls/you aren't sure how to get from Point A to Point B is an inefficient use of time and money.
Most lawyers I have talked to stress the importance of coming out of law school as a generalist. The law schools are telling the law students that they need to specialize now. Maybe the MBA sounds attractive b/c you think it will get you into business law. But in reality, I'd rather take do what the hiring partners are advising-- they're the ones coming up with the paychecks at the end of the tunnel, not the law schools or the MBA schools.
As far as pursing them separately. It is a judgment call. Also, how much time between degrees? I can see it making more sense for you to do one, wait 5-10 years, and then the other, as a result of life experience and introspection. But doing them concurrently or within a couple years of one another would tell me you're not sure about how to get where you want to go with your career just yet. I would see it making sense for a lawyer to to get his MBA after several years of law practice in taking a new direction with his career, and possibly going into a non-law related field.
Good luck with whatever you decide. But I really think you owe it to yourself to figure out what will be the shortest path to get you where you want to go. I personally don't think a JD/MBA is the way. Others may completely disagree, but I was contemplating this exact question not too many years ago. A lot introspection and talking to people got me to realize that it would not be a good use of my time or resources.