I live in Spain and have cruised the Western Med from Barcelona and Rome a few times. If you are only going to do this once I would recommend Rome in Limo for an excursion to Rome. For La Spezia I love going to Pisa but perhaps a Pisa and Florence combo excursion for architecture and history or Cinco Terre for scenic views (lots of walking typically). For Naples Sorrento is beautiful, Pompeii is impressive if you have never been but Herculaneum is more intact and gives you a better impression of what life was like. For Mallorca an excursion to Soller and Valldemosa would be good or just wander about in Palma city. If you get the chance to go to Monte Carlo from Marseille, do it, perhaps taking in the changing of the guard.