Well, two weeks later, I've played with putting some extra fill in the bass ports of my VR5s. At first I seemed to tighten the bass up nicely but after a while it did not sound so right to me. So I started playing around with pushing the stuff right up inside, just inside but at bottom floor, and finally in various distances on the port (which is not as deep as I had imagined). Yes, this stuff does change the sound, and where you stuff the stuff, so to speak, matters. However, to confirm a final choice, I put some Holly Cole samples on repeat and did a firmer comparison between the various locations on the exact same pieces of music and decided, ultimately, that I prefer the Vons stock -- no additional fill added. Ultimately, while I could reduce the bass level, and even get it to the point where it sounded as if I'd rolled off a bass tone control, for those who remember such features on amps, the music across all frequencies just seemed to lack a little life and space in presentation. It was not just the bass, it was the total balance, and I felt music sounded better all round with no additional material in the bass cabinet. YMMV.
If you are constrained by positioning (which I am not really), the extra fill can be an interesting and really cheap way to adjust the sound in your room but for me, with the fronts some 56" out from any walls, the 5s just sounded more natural without extras.