The only port I'm familiar with on your itinerary is Barcelona which is really easy to manage yourself. The ship will run a shuttle which stops by the Columbus monument which is at the bottom of Las Ramblas ...if you walk up this tree lined street with shops and stalls and street entertainers as far as a big roundabout ...on the right is a large department store called El Corte Ingles which has the stop for the hop on hop off tourist buses outside...they run a northern circuit and a southern circuit ...we've only done the northern circuit which covers the Camp Nous football stadium (which apparently is very interesting for those interested in football!) and also Gaudi's cathedral. We sat on the top deck with our commentary headphones and thought it was very good value for money (19 euros each, if I remember correctly, for the day) we had very good views of the wonderful quirky architecture at roof level. It eventually drops you where you got on so you can then stroll around the back streets heading back to the monument where you get the shuttle back to the ship. Lots to see.
From Naples we got the ships trip to Pompeii which was well worth the cost.
perhaps someone else can help with Sicily, Corsica and Toulon. We have been to Sicily but to Messina where we did the ships trip to Taormina which also was a very good trip to do. Hope this helps a bit!