Are subs worth the price for music?

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...

I concur with soix  Once I finally got a pair of Velodyne HGS-10s integrated with my KEF LS50s, it opened up the sound so large orchestrations that had been the downfall of the LS50s are presented convincingly.  Adding the subs changed the entire experience.  I use a Velodyne SMS-1 bass manager to low-pass the subs at 50 Hz with a 24 dB slope to minimize overlap; the SMS-1 also provides acoustic room correction.  The LS50s are driven by an Ayre VX-5 Twenty amp, the HGS-10s by the SE outputs of a KX-5 Twenty preamp.

Well, maybe the Speaker can go down to 26 Hz,

but your source, amp, and all PCs, ICs, and SCs will need to carry that clean and low of a signal to get you that 26 Hz to your ear. Also, If the bass player/musician, or the music you listen to is not playing below 26 Hz, then you are not missing out on anything. 
O/w, 26 is just a number.

That said, I have some Dynaudio Contour floorstanding speakers that go down 32-35Hz. But I still felt like I was missing something, missing the “presence” of the band and the music.

I’m not an HT guy, but I found that using just one quality sub, placed b/w my Dynaudios for music listening, gave me that extra LFE that allows me to feel like I am more present “in the room/venue” with the band.

I use a Zu Audio Undertone, a sealed sub that down to 14 Hz or so. That is more than I need, but the sub is so good that it has pretty seamless integration. Besides, I’m only integrating LFEs, which are more omnidirectional.

So, I would makes sure all your gear upstream is good enough to produce LFEs down to 26 Hz and you are listening to music frequently enough that goes past 26 Hz. If that is the case, and you are still unsatisfied, then check out some high quality subs that are robust under 26 Hz, like the Zu Audio sub.

Low frequencies are part of natural ambience that's everywhere, and subs bring that stuff to the room...not simply the low notes, although clearly that's a good thing, but the sense of reality that's part of live sound. I use 2 RELs with a small tube amp driving efficient speakers, and it sounds like real music.