|Thanks Derek, interesting point that I hadn't considered. And it may well be one of the reasons that today the folder opening speed has improved significantly. Can't be sure because the two changes between Before and After were:|
1. Used the registry cleaning section of CCcleaner
2. Rebooted (again).
Maybe there were some invalid shortcuts amongst the many entries CCcleaner deleted. (I didn't examine them, as I've grown to trust the tool, and always take the SR option anyway.)
But amongst other possibilities (and research shows them to be numerous indeed, as thomasad said) I still wonder if it's somewhow connected with my external drive. The latest one I added some months ago was a WD 2 TB unit. Unlike my earlier WD 1 TB 'My Book', this seems to get 'powered up' sometimes, even when I'm not opening any folders or files on it. Because I opted out of installing all its accompanying software (for backup, etc, that I don't need), I'm unable to configure its 'power mangement', so I'll never be sure about this speculation.
And all that may be irrelevant anyway. I'm just pleased that - for now at least - the problem has gone away!
Terry, East Grinstead, UK