I'm also confused by people reporting quality gains, or expanded gamut from the 16 bit driver. As far as the range of color goes, that should mostly be the domain of the profile. 16bit vs 8bit will affect the gradation of colors within that defined space. I would expect to see a minor improvement in some subtle transitions, but there should be no drastic color change. It would be troubling to see a shift in colors when doing a conversion from 16bit to 8bit in PS, and I would not expect there to be a shif in the print either. The explination does seem to be that the 16bit "export" uses a different data path, but why this should yeild radically different results from a standard 8bit workflow is something I would like to understand.
I agree that the difference should not be dramatic, and it doesn't appear to be.
Did some tests, comparing RAW files printed at 8 bit with regular driver and 16 bit with plug-in, both with iPF5000. Hard pressed to see ANY difference ?