Just did it, added another layer of stuffing.
Apparently when I first did the mods I didn't make very even coatings in both sides (Right had a good bit thinner layer than the left) which isn't surprising since I did all the mods in one shot instead of sleeping before work.
I must emphasize this, MAKE SURE YOU LAYER BOTH SIDES EVENLY. I was blaming this on likely damaged hearing, but I kept swearing the right side was louder (and looser) than my left.
The extra stuffing had the effect expected (Less bass, seems more controlled - whether that's true or it's due to the effect of the bass coming in at a lower volume due to stuffing, I'm not sure), and I think I got the sweet spot (for me) this try. (Basically the entire cup is full of loosened fill now - not packed, I made sure it was light and airy. Whether this will matter much, I don't know as I haven't tried it.)
Opinion: STUFF EVENLY, I just want to make this point again as it provided a notable improvement to my ears. Even unevenly stuffed the sound was great, but now that things are a lot more even - it just sounds so much better. At my current level of stuffing my bass exists, but it isn't amazingly powerful (to get the vents to shoot out air I'd probably have to up the volume to pain levels now) - which is fine with me since it DOES exist (way more than my HD201s).
I don't know how it works, but stuffing has made me up my volume to get the same level of sound as I was previously using. The main thing though is as I crank it up everything else (mids/highs) is louder. I won't say more defined - they were there and detailed before but so hard to hear. (esp the strings in "The World", now I hear them quite well with all the detail still intact).
Familiar Songs tested on:
Gorillaz - Kids With Guns 320kbps (Bass)
.hack\\SIGN soundtrack lossless .flac
-The World (Strings - mids/highs)
-Magic and Sword (detail [morrocca? strings, few other instruments I can't name offhand], Bass)
+others