I was looking at this the other day, in short DD is the command you want, it just clone copies it straight over but once done you need to mess about with FSTAB to get it to boot correctly as the UUID's are wrong.
You could also rip a live USB and use gparted to copy the partitions over one by one.
I'd probably say unless there is any system config which is absolutely "of the essence" a clean install would be the cleanest solution.