Should one plan a trip to the Cinque Terre in late October/early November?
me,
The Cinque Terre will certainly be less crowded then, but the main issue at that time of year will be weather. It could be rainy and it will be cooler, so beach time won't be as attractive. Hotel prices may be a bit lower, so there are advantages to travelling then. The boats may not be operating that late in the year, but the local trains will be.
You could still plan a trip at that time of year, but be aware of the limitations and check the weather.
I agree with Ken regarding the weather.
My mom & I visited CT in October (some years back), & we were fortunate enough to have good weather.