Are subs worth the price for music?

My current speakers are Vandersteen 3A's. I consider them to have a good, solid low end. Specs say 26hz, -3db, if I remember. That's lower than most any music. I'm considering adding a vandy sub, possibly two to the system. My question is, for strictly music, are subs even worth while...$$$......if so, why? What could I expect that's different and/or better than what I'm already hearing..............No experience with subs and music, so forgive the lame question for those of you who already use them.