Thanks for your thoughts!
My workflow is to scan to "raw" in VueScan, assign the profile, and then edit in LR4 without converting the profile. This, I figure, leaves me with the original scan data and does the least destruction (none!). LR4 seems to handle the device space profile and edit very well. When done, I render into the appropriate space.
I used the CCSG as the target, and scanned it with the same raw (VueScan) workflow. I made the profile in PMP5. Today I tried version 4 (I had used version 2), and also made one with "large" profile size, and one with "default". I am getting the same result: the profile shows up in ColorSync Utility, but not in Preview.
I haven't used Epson Scan since, at least when I tested it out a few years ago, I couldn't get a reliable raw scan. I also remember not being able to lock the software down to a "wide open" state, which is what I do with VueScan. Maybe it's better now?
Any further thoughts?