The comfort "improvement" with the velour top mod is indeed debatable; there is nothing smooth like a good pleather material i.e. the protein pleather used on Hifiman earpads (except maybe Audeze LCD3 lambskin). However it does help cool down and stop sweating of your ears, and distance your ears a bit more from the drivers (good news for those with big ears but who hate velour pads).
The main point of the velour top mod is the sonic improvement though. I cannot understate the fact that it magically removes the "sealed closed-in sound" of pleathers, and makes all the sound suddenly open and out of the head. The "believability" of the 3D imaging is boosted incredibly high, even though the soundstage might sound similar in size with just the bare pleathers. That on top of the fact that it does not alter the innate tonal balance of the pleathers makes it a very strong addition in the Jergpad modification steps.
Ah! You're killin' me man. Now I want to go mutilate another pair of pads, haha.