Hi Jules,
Unfortunately I'm unable to confirm whether or not you would get your return on investment because I'm in my 3rd semester of an MSW right now but I'm also 51 and looking to change careers. I also want to become a counselor and from all of the research I did prior to applying for an MSW program, I realized the only way I'm able to talk to patients one-on-one is to get an MSW and be licensed as an LCSW.
Regarding the biology question, my MSW program only has Social Work classes in it. The math, science, etc. courses I were all completed when I completed my Bachelor's last year.
I hope that helps!
~Megan