Hi we visited these ports on the Island Star last year. Genoa we went to Portofino on an excursion which was great but other people told us the walked off the ship into town and was easy. Marseille the ship berthgs in the docks area which is a good distance from the town. Island cruises provided a shuttle bus into the centre which hardly cost anything and you could come back any time through the day , that was good. Barcelona is the best - you berth and can walk across the road right into Las Ramblas and the centre. Valencia , The cruise line gave us information on getting local transport from the port but was a little confusing. We were with other cruisers so we all worked it out together , it was a laugh really but just be sure you know all the facts when doing this as the bus driver spoke no english and luckily myself and wife speak spanish and some old guy on the bus gave us some information. Beaches, cant remember any nearby in marseille but wasnt looking for them, there was in Barcelona but not sure how far - hope this is of some help, Enjoy - its a great itinerary !
Thanks very helpful information,glad to hear you enjoyed your cruise.