Thanks so much Annhig for your tips. After some deliberation we have decided to join a small group with a tour guide to visit both the Vatican on one day and the Colosseum on another. That way we still get to see both while avoiding the long cues (we have been assured). Yes, I have heard of the galleria Doria P. and will definitely consider visiting it. Thanks to the amazing support of so many Fodorites we have a pretty good idea of what we would like to do during our three days in Rome. One can plan only so much ahead of time and we also would just like to enjoy Roma as a spectator. These three days will be followed by a stay near Perugia so there will be plenty of other opportunities to visit several beautiful churches and museums there as well. Can't wait! Thanks again!

What small tour group are joining?

We booked with Roma Experience Tours at the advice of friends.
https://romaexperience.com/#!tours=book_tour

Their prices are very reasonable in comparison with other tours. I subsequently checked their reviews with Tripadvisor (see below)

http://www.tripadvisor.com/Attractio...ome_Lazio.html

sounds like a great trip, Elizabeth.

buon viaggio!