"Anyone have any thoughts? I realize it will be about a 2.5 hour trip each way."
First, it looks like you're under-estimating the travel time of the combination driving - train itinerary that you're proposing.
Second, driving the entire route, instead of doing the combination drive and train, may give you a shorter travel time--usually a hazardous statement to make about driving in Italy, but in this case it may be correct.
Consider this data: The station to station train time from Florence to Vernazza is 3 hours or more, each way; and that does not include the time to get to the station, buy tickets, and wait for the train--on either side of the train portion of your trip. Now, I realize you're not planning on getting the train at Florence--but the above times suggest that your 2.5 hours each way is unrealistic, for the combination drive-train scenario.
Getting the train somewhere else probably won't shorten the trip: you'll still have the driving time from Rignano to wherever you catch the train, plus the waiting time for the train, etc.
Driving all the way would eliminate some of this. Of course, driving you may encounter traffic slowdowns in the morning and evening rush hours, or at other times, which would change all the travel times and the above comparison.
Lastly, some travelers here have found GPS helpful in reducing stress and lost time navigating the Italian road system.
