I'm going to buy a PA for Vocals only. Is it worth spending the extra $ for the JBL JRX125 speaker pair or get?

You Dont have to worry at all. The 125's would be great if you were trying to be a DJ or something where lots of volume of b was necissary but you have nothign to worry about. You can get along just great for a long time, with tracks and even a small band with this PA.