Thanks for that excellent demonstration photo. You should make a poster, would sell in droves to giclee makers.
Yes the spectral reflectance thing is one of the big bugaboos, not to mention the tendency towards metamerism which that and other effects bring to inkjet prints. And there's this newly recognized kid on the block called "subsurface scattering" which is a close cousin to spectral reflectance.
Hey Roscolo, I'm feeling kinda poorly about having pitched that Colorchecker to you. It works for my wife's very punchy pastel work (yes it's possible!) but have never tried it with subtle colors, or in situations where it's necessary to reproduce the subtle surface qualities and shading of the original media on the giclee media.
I just tried out the Datacolor "SpyderCHECKR" which is a sort of giant sized Passport. It's got the exact same patches in a different arrangement, plus an additional 24 patches in much more subtle shades. And yes, those deep-blue and crimson-red patches that the Devil put there are still present.
It's more trouble to use. You have crop it tightly in Lightroom, then send that image to the Datacolor software. But what it does is not create a DNG, but rather a lightroom preset with the controls in the HSL panel and elsewhere all tweaked around. You need to have the same Lightroom profile applied as when you made the preset. I have to say the match looked not too good last night under tungsten only, but this morning with sunlight coming through the windows it looks pretty decent, relevant to the tlooknbill was saying. Would NOT want to say this is "the solution" but it's an interesting approach. It also gives you a choice between what it calls "Saturation" and "Colorimetric" intents, Colorimetric seems to be more subtle.
I have also found that with the X-rite Passport, I can considerably get away from the slight oversaturation by playing with just the Hue and Luminance controls on just the red channel and magenta channels. I think the X-rite Passport might be giving us a Saturation intent, rather than a colorimetric one, but I see no way to specify anything like that in the software.
Also, I bought one of the QPCard201's from BH Photo and the darned thing only works through .jpg's! Good grief, what's that about! You apparently need the 203 model (or something) to work at the RAW, and nobody in the US seems to carry it. Sigh.