Thanks Stuart, I will indeed hope to be installing the old disk too, with carefully chosen partitions that are rarely accessed, to mitigate the head noise. I am aware I'll need to zap its partition table and repartition to bet new UUIDs, but you've made me think of a new issue...
I wonder, will the cd booted environment in which I perform the dd copy get upset by the fact there are duplicate UUIDs, even if not mounted. For example, If I type
ls -l /dev/disk/by-uuid
...then it shows me the UUID to device mapping, so the system is at least aware of unmounted UUIDs...
@Eric, also thanks. I may play it safe by altering fstab as you suggest, and/or I will check out Clonezilla too.