If you can arrange a good tour guide, it is well worth the money. They will get your reservations to Vatican, Collesium, etc. ahead of time and save you waiting in line. Also, with a guide and driver, you won't have to worry about transportation. They drop you at the closest point and come back for you when you're done. We had a wonderful guide in Rome a few years ago. We arranged the tour from home (with the help of a travel agent - do they even still exist in the age of internet do-it-yourself?) and I don't remember what agency she worked with but she was fantastic. The same travel agent arranged for our guide in Paris who was terrible.
Don't miss the Galleria Borghasi (probably didn't spell that right). Lovely grounds, statues, art work, frescoes and not very crowded at all.
Have a great trip!