Well, I can´t help you with all your stops, but I have some ideas regarding barcelona and Rome.
In Barcelona: Try to get a shuttle bus that takes you to the port exit. The hoho-bus leaves at colom. The bus company(Barcelona Bus Turístic )offers 3 tours in the summer time, don´t take the one that goes past olympic harbour(green line)... The other tours take you all through the city. Please keep in mind that when you get off at major sights (f.e. Sagrada Familia) there may be long lines for getting back on one of the next buses. Prices are: 20 Euro per adult per day, 12 Euro for kids age 4-12.
Rome is another matter altogether. The port isn´t in Rome, but in Civitavecchia, a med town about 1 hour by train frome rome. So first you need to get to the train station from your ship. you can either take a taxi, or use the shuttle to the port exit an walk from there (about 15 min walk). The train to rome on a retour-ticket is 9 Euro p.p.. Take the train to statione termini (main station in rome) right in front of the station leaves the 110-bus, the hoho in rome. The bus costs 16 Euro p.p./day and 13 Euro for kids age 6 - 12.
Please keep in mind that you´ll need enough time to get back to the coast and your ship.
November 2005 - Costa Marina (Spanien und Kanaren)
Mai 2007 - Costa Victoria (öst. Mittelmeer)
Oktober 2007 - NCL Gem
November 2007 - Costa Fortuna (Karibik)