@Bud,
well, maybe it wasn't that bad idea
I took that risk and altered calib.rcs file without altering the CRC. The device didn't brick!
I have progress - I have further reduced spatial pixelation (temporal I reduced in my previous session, see above), including raw noise and calibration stability by factor of 3 at least. After all, I only have this nasty horizontal lines like from humming on old TV and since all other noises were reduced and this one - not, it is now the main contributor
Well, how I did that? Naively, as always...
I discovered there is default calibration data for the Z3 camera in the folder.
I pinned my attention to the fact that double float values in actual calib.rcs files are mostly, replica from the same resource keys in the default file, but ... they are trimmed by factor of 100 in decimal accuracy. So, actual calib.rcs uses the same default values, but of smaller numerical precision. I therefore assumed that this would lead to numerical instabilities of all sorts, lower calibration accuracy (spatial) etc.
I copied the values from the default calibration files into matching keys of actual calib.rsc files and voila! I have it after reboot.
ATT.: to those who are seduced to try this!
Always backup!!!!
This will not increase sensitivity or reduce temporal noise. This only improves calibration cycles and makes it hold longer and more accurately. In my case, I have over 1 minute stability in 2C temperature span (10 seconds before this modification were enough for spatial noise start to emerge noticeably, so had to always calibrate in a dark isothermic room
As a bonus, I can now see my shadow in matte surfaces in isothermic environments... this is pretty faint signal actually, and before it was not possible to notice.
Thanks all for your neverending help, support and understanding,
I am carrying on further experimentation!
TODO: remove those fracking horizonal temporal raws noise.