The location of the spots on the images give a wealth of information about the cell constants leading to very precise values, if you know your wave length and crystal to detector distance. Intensities, not so much.
I think that there is a fair amount of imprecision here. For example, what is the usual precision of the beamline-defined crystal-detector distance, and of the wavelength? Even 1mm/100mm total distance could have its effect on cell parameters, and I don't think refinement of the distance based on trigonometric distortion has a very sharp minimum, although please correct me if I am wrong (how is the detector distance calibrated, anyway?). Even having an oblong crystal might change the distance by ~0.5mm or so. But this is theoretical, and I think you have much more empirical, real knowledge--what are the levels of precision on these fronts, and how precisely do we know cell parameters from experiment (I thought it was pretty imprecise)? Jacob