Are subs worth the price for music?

Worth it? 
Your speaker designer / manufacture certainly thinks so. Even though some of his speaker are equipped with separate equalized low frequency systems they are often showed with his outboard subwoofers and has just introduced a new model. Vandersteen and his dealers understand low frequency reproduction. An outboard Vandy sub will be compatible with your 3As and any future Vandersteen mains upgrade. You can't lose.

-3dB @26Hz. 
Most rooms need that -3dB compensated for. Your room may need a flat low frequency or an increase of +db. The main speakers locations are usually not the best locations for low frequency output to integrate with the room despite the speakers designed ability. The room usually dictates where the location of low frequency origination should be. These locations usually provide a better response at the listening position and a reduction in the rooms bass nodes. 

What can you can expect?
If setup properly you should hear very little difference until you turn the sub/s off. The low frequencies will integrate with your speakers and you should hear improved separation. Integration with your room in the form of seamless increased low frequency gain as it was recorded and not falling off. You'll be surprised at the amount of low frequency that is actually recorded on a variety of recordings. Hearing it well presented in your room is what the subwoofer does.

Lastly, its simply way more fun.        

Thanks for the inputs folks................I remember some years ago with a dealer demoing a small pair of B&W speakers and an attached sub. I listened for a bit and then had him turn off the sub. There was a difference, but not earth shaking and I doubt the monitors could get much below 50-60 hz without the sub running. I guess on most music what I'm getting from the 3A's is about as good as it NEEDS to be 90% of the time.

Don't really need to hear the semi rolling by the studio outside :)

I'll play with my setup and treatments a bit and see if there's more to be gained in that respect...........Cheap and easy way out...............Maybe I'll keep an eye on Ebay for some Vandy subs..........Christmas is coming :)

Happy listening!!

I used to be in the @williewonka camp, but I've since gained a much deeper appreciation for what subs bring to the table after hearing demos in a couple different systems.  Both systems were high end with expensive full-range speakers, and in both instances the systems started out with subs engaged and sounded fantastic.  Then the subs were turned off and it was amazing how much changed.  Obviously bass dynamics were not as impactful, but what was really surprising was that in both cases there was a significant reduction in perceived air and space, and the whole soundstage compressed and sounded like it had a lot of the life just sucked out of it.  I had no desire to listen to either system without the subs after that.  I can't explain exactly why subs seem to significantly impact aspects of sound other than just bass, but they do.  Anyway, for those who still think subs are there to create rumble and handle pipe organs should seriously think again.  And with the growing number of processors out there to take the pain out of sub integration this has become a no brainer for me.  Plus there are direct sellers like SVS that give you a 45-day trial period so you can see if I'm a liar with little or no risk.  There's a reason Wilson builds $25,000 subs, and it ain't just to pair with Duettes or Sabrinas.  Anyway, FWIW. 

As a prior owner of the 3a sigs and 2wq subs, I can attest to the benefit of adding subs, especially Vandersteen. Remember, using Vandy subs will allow your amp to work more efficiently when coupled with either the fixed or variable crossover.
If it were me, I would consider changing speaker cables to Audioquest. The GO-4 is relatively inexpensive and they work wonders with Vandersteen. A local dealer might have a set for you to trial.
When in doubt, contact John Rutan (audioconnection- his Agon moniker). He knows Vandersteen and can give you the best info, and not try to sell you something.
Bob

Subs can be great for music, though agree proper set up is crucial. I had great success with Vandersteen 3A and Genesis sub some years ago...