Thanks again, Saab Dastard. I really do hate to be a bore but my lack of understanding obliges me to be one. Would you be kind enough to explain what eventuality was worrying you when you recommended making a file-by-file copy of my data AS WELL as the easier (duh!) regularly updated snapshot?
If ever the safety copy is used it will certainly be used to "load up" my old machine's programs, settings and data onto a new machine with a much newer OS.