I did my masters while working. My job at the time paid for it, and there was a good school in the area. I found it fun because I was exposed to things I wouldn't have gotten exposed to in my job (programming language design, automata theory, etc...), but those things also didn't change my salary or future job prospects.
If you find learning in a structured environment fun and can get someone else to pay for it, a masters may be right for you :)
If you find learning in a structured environment fun and can get someone else to pay for it, a masters may be right for you :)