Anyways, are you sure when you put those hybrid CD's in iTunes, it is the CD layer that you are importing?
Yes, my DVD drive in my PC won't play the SACD layer, so I must assume that it's the CD (Redbook) layer that it's accessing.
I did initially rip the disc into iTunes using a default import setting of 256 VBR. I've since replaced those files with Apple Lossless Audio (still .m4a files), and you're correct: a 4:30 song comes in at around 30MB.
A subsequently sync to of my iPod included these new files without incident.
FWIW, Windows Media Player is meant to be one of the few software players (AFAIK), that supports the HDCD coding, and when I played this disc in WMP11 (directly, not ripped), it displayed nothing to indicate that it was HDCD, nor did it sound any different than the same track being played in iTunes (lossless format).
IMO, "HDCD" is marketing hyperbole, in regards to audible differences. As has been said, it might be measurable, but it's not necessarily audible.