The inner port is at the bottom of las ramblas and there is a shuttle to the outer port area where the bigger ships dock, a TAXI is not that expancive.

We had a large group and ended up eating at http://www.tallerdetapas.com/ one night which was good enough for a touristy location, if you search the net there are some off the beaten track places that sound realy good but were not suitable for a larger group, if you are adventurous they may be worth a try.
You could try a visit to the magic fountain for the rearly evening it was not running when we were there.

The subway/train bus are easy to use, you can get a multi use(10) ticket for 6(ish)eur thats enough for 2 people one night. return to the airport and 3 other trips.

Also get the Aero bus or the T10 to get into town from the airport lot cheaper than a taxi

If you have a full day then a trip out to Montserat is well worth it.

Naples, I think a must do is Pompeii folowed by Sorento and if you must Capri. Last time we were there we took a walk through the town to the Museum of Archioligy(sp) very interesting place but not a lot to see during the walk(45mins) if you don't have a guide book to tell you where the things are(lots of odd ruins etc.)

Rome DIY by train is easy, there are a few posts that detail this have a search. I think rome is best done as vatican or ruins other wise it is a bit of a ruch to pack it all in.

Livorno, you can DIY the train to Florence not done it, we did a private tour by bus a few years back which included tickets to the Acadamea to see David.

Liz

Have a look at the sticky DIY Excursions topic at the top of the forum for some ideas.

Rome is very easy to DIY and you can visit what you want.

luci

Anotehr tip from MSE on the bus from the airport

http://forums.moneysavingexpert.com/showpost.html?p=9412707&postcount=11