Lola, Nigel, et al, thank you for the additional considerations. Another person mentioned the ability to sight see that a train offers.
The plan is to begin the 5 week trip in Barcelona or Girona and conclude in Paris.
The following is why I began to consider a car:
-I was set on using trains, because we were going to stay in Barcelona (6-7 days) and fly to Nice, but now we are leaning toward staying in Girona. I discovered the train ride from Barcelona or Girona to Nice is 8-9 hours. If we stay in Girona and choose to take a plane to Nice we will have to back-track to Barcelona (1.5 hour drive) and spend the obligatory extra time at the airport. Neither of these seem like great options.
-The cost to rent a car in Barcelona and drop it in Nice is quite expensive because it will be a short term rental (not a lease) and the drop off fee will bring the total to around $1,200.
-There are no direct flights from Girona to Nice.
-If we stay in Girona it may be nice to have a car.
If we don't do a lease car, perhaps there is a car hire service that we could use from Girona to Nice,but I'm not sure. The drive appears to be 5.5 hours (3 hours less than train).
Once we get to Nice, I feel fairly confident that our trip can be completed by train.
Lots of considerations!