Thanks bertiecharlie and stalion for those links. They both advise against removing the \ServicePackFiles folder.
As for HDD size, I've got 13+60+60+80Gb but the small one is partitioned so that Windows is on a 4Gb "drive" -- which used to be plenty. Seems like some housekeeping is needed. There's a few other small applications on the drive, which I can move elsewhere.