We are a group of 3 relatively able seniors, one of whom is a seasoned driver in Italy. Should we rent a car for a 2-day trip to visit the Cinque Terre area in February or use public transport?
Cars are not very useful in the Cinque Terre. Parking is limited, and is usually outside the village, which usually means a long, steep
climb back after your visit.
The train however just takes you directly from one village to the next, and runs quite frequent. And you can combine the train with hikes along the paths, and even a boat ride.
Agreed, a car is an expensive burden in this scenario. Take the train and change - probably in Viareggio - to get to La Spezia.
Then use the local train schedule to specific towns. Depending on the town it may be possible to buy a ticket to the town you want or it may complicate your ticket search - use La Spezia for the clearest options.
Weather in February will be cold - depending on where you live - and subject to rain and wind. Check the weather right now for a real time report of what it might be like. I don't think the ferry starts limited service until March so the train will probably be your only option.
Hope that helps,
=Tod