I'm not a news or law librarian (yet!) but I am aspiring to law librarianship. To address your concern about the availability of jobs: there is just as much whining about the job market for law librarians as there is for librarians in general and academic jobs at large. I did a lot of research before I decided to pursue this. I am not sure if it will pay off, so I can't help you with that, but I would recommend you check out articles online by the Library Journal, read the section on librarians in the Occupational Outlook Guidebook (BLS.gov). Any job in an academic environment is tough to get. The employers of law librarians, like universities, governments, and law firms, are all strained right now. You need to look at the jobs people are qualified to do with that training if and when they do not get the specific professional job they hoped for. To me, working as a paraprofessional in a firm that did work I supported or in a small-town public library is acceptable, even if it's not my first choice. Depending on what school you go to, the MLS/MLIS/MIS degree equips you with technology skills and service training that is transferable to many different positions.
I completed an MA in history after undergrad. I was fortunate to be allowed to take graduate courses as an undergrad, so the MA was not a significant expense or hardship. I do think it was tremendously helpful. Graduate research was on a completely different level than undergraduate research. I also found that the MA gave me more time to talk to professors about their research, work in the department, and work closely with librarians, archivists, and academics. I don't think I could have proceeded confidently into such a specific professional program before the MA, but you may be more mature than I was. I would recommend an MA if you love the subject, are interested in the coursework, and it does not pose a financial hardship. Even if you decide to pursue librarianship afterwords, you will be a more competitive applicant and once you are done you will be more desirable candidate if you have a subject area specialty.