return on investment MSW vs Caseworker salary

[julesevar]

I'm 51 years old and recently have been working as a caseworker for about 1 year and 1/2. I used to work in state government.  I plan to work until I retire when I can get medicare.  I am interested in going into Social Work to do therapy.  I enjoy my casework job and recently got a substantial raise.  I could apply to several online MSW programs. I have a local state school that is around $35,000 tuition for the whole program. Other programs that look interesting charge upwards of $60,000 or more.  I have done research that the lower end of the spectrum for the MSW and my salary are similar. Now I have a relative clinical social worker that works for the federal government who makes similar to a well paying MBA. Not that I want to get a MBA. I was just wondering if anyone had thoughts if it would be a good return on investment of between $35,000 to $65,000 tuition to go for the MSW? 

Of course I would have to be accepted into any program, but I think that I could.  Micro-economics was not my forte and I know there is a way to figure this out based on a economic graph. 

Another question I have is how much biology is required in MSW programs. I haven't taken a biology class since high school!

Thanks in advance,

Jules Evar