Ok I just stuck the foam rings back in because the sound became congested. I think it has to do with the spacing of the ears and yeah it may impact treble somewhat, I didn't notice much. But removing the foam and thus placing the ears closer to the drivers DEFINITELY impacted the overall sound negatively.
I would recommend not doing the foam mod ALONE.
I'd tend to agree with you, but it makes the bass bloom more (dunno if that is the correct term), and you have to get used to that. I had to... Personally, I think it is better w/o the foam rings, but I did like the drier and less intimate/congested bass with the foam rings better.. As I remember, but that was months ago... And with the HE-500 btw.