I am please to inform that this 10 years old ticket can be closed as fixed. Gdal_translate from GDAL 2.0-dev (2015-01-13) transfers the TIFFTAG_MINSAMPLEVALUE and TIFFTAG_MAXSAMPLEVALUE tags unaltered into a new tiff file. If they happen to be wrong for example because of cropping they can be written back with the gdal_edit.py utility.