So.... I think it's safe at the moment to say that processing these files has a substandard answer in the mainstream commercial programs such as ACR, C1, SP etc. There is the different approach (with its own, lesser problems) available in DCraw as a command line program and a few GUI front ends for it with their own interpretations of command-line strings for the initial processing such as free programs like Photivo and LightZone or commercial versions such as Helicon Filter and OloNeo Photo Engine.
All have their own interfaces which range from simple to utterly complex and confusing, or weigh the program down with extraneous functions which have nothing to do with the actual task of processing raw files.
With my mind spinning from trying to learn all these different interfaces and functions while trying to get the best result possible for the much maligned X-Trans sensor, I sat down this morning with a "What if?" thought in my head, namely that if the best straight, unmodified demosaicing available at the moment is the inconvenient to use DCraw, then what about taking one or the DCraw-based GUI programs, have it do a basic, unadjusted raw conversion as a linear raw (choose that if available, or in LZ disable or remove the X camera "raw tone curve" by unlocking and disabling it), save that dark, flat & ugly image as a TIFF, then simply adjust that in Photoshop (or ACR, LR, Photoshop, whatever).
The rub of it - it works perfectly well. A basic RAW conversion of a well exposed file (nothing too blown or underexposed) dropped into Photoshop & hit with Auto Tone (in Ps if you're feeling lazy) yields a beautifully rendered 1-255 spread of tones. If your image is less than perfect, then a visit to ACR Curves will do it plus give you the additional controls that make that program so desirable and quick, but without Adobe's hideous attempt to turn the file into an oil painting.
For the moment, and despite the extra space required for Tiff files (though they can be saved as DNG in ACR to save a bit of space), this gives what I consider to be the best interpretation of the X-Trans raw available until Adobe, SP C1 etc get their collective acts together, and I can now leave this time-consuming chase and get back to using the camera without worrying about the end result. Doing things this way means that no extra $$ need be expended - LightZone does the job and it is free.
I've attached the two images I've been using in this torturous process thus far as unresized jpegs saved at 10 quality plus the same images processed in ACR. 100% is revealing, 200% shows graphically where Adobe went wrong, and while the artifacts of both methods don't provide too much of a problem in normal usage, the biggest problem I find with ACR is the way whatever it does to smooth things over kills the colour depth and gradation, and their "solution" of boosting saturation and contrast to compensate is pretty crude. This is the thing which does affect the images at normal usage size, and what I have the greatest problem with.
Anyway, FWIW here are the results, and I'm off the case now. I'm happy with these results and the speed and simplicity with which processing can be done.
Edited by Fred Nirque, 27 January 2013 - 02:53 .