Thanks, @ashleykaryl; Yes, what you say seems sensible.
I just don’t want to take the step of moving all my Addons (I’ll back them all up first, obviously) on the first machine to, say, DropBox; and then find that there’s no way of getting the second machine to go and get them there by default since the only wording of the Preference in question is ‘Move…’
In other words, I need to be sure that RW 7 doesn’t move the second machine’s (not previously ‘synched’) own Addons there and overwrite the files put there by the first.
Synching algorithms are notoriously tough.