Are you thinking about next year or leaving in a couple weeks?
I was recently in Barcelona and (for the first time) the French Riviera. I was lucky with weather, mostly sunny and not a drop of rain in late March (2 weeks). With the exception of Alicante, I've been to all your places.
Valencia is well worth 3-4 nights, beautiful architecture, interesting museums. If you are thinking about next year, consider going in March instead. Valencia has a huge festival March 15-19, Las Fallas. It's unlike anything else I've ever seen or heard about.
Barcelona has become, after 3 visits, one of my very favorite cities so I can't recommend it enough. A week is not too long there.
The train goes through Girona and Figueres. Girona has a well-preserved medieval center. Figueres has the Dali Theatre. Both are half day visits. Consider staying in one and day tripping to the other. Perpignan is on the way, don't know if it is interesting or if it's simply where people pick up a car on a Spain-France itinerary.
I spent 2 nights in Marseille only because it was my gateway airport. I was surprised by how much I enjoyed 1-1/2 days there. I felt I'd seen/done most of what I wanted. Because of the mistrals, I didn't want to spend more time in the area, but later in the year there are certainly other places that would have called to me - Aix, Avignon for sure. I think they can be day trips from Marseille, but may be worth overnight stays.
I was in Nice for 5 nights. I was less excited about Nice than Marseille, but it was a pleasant enough place to be. I stayed near the train station. It's definitely not the best part of town, but very convenient for day-tripping and easy walking to the sea shore, with nearly all the sights and "best bits" in between. It's a good base to day trip by train (mostly) or bus to many interesting and/or charming villages, beautiful estates of the rich, terrific art museums - Picasso, Chagall, Cocteau. I visited most of them and in hindsight I'm glad I chose Nice as my base. There are many choices for hotels, many more for good restaurants, lots of cafes and several good pubs too. There are major stores which was a blessing when I needed to buy ordinary "stuff" that was either left at home by mistake or lost somewhere in transit.