We just returned from our first trip to Italy on the RS Heart of Italy Tour. We arrived on a Saturday and before we met the tour on Sunday, we booked tickets to the Borghese Galleria. Simply stunning! You get up close and personal to artwork that takes your breath away. The walk through the Villa (the park surrounding the Galleria) was lovely, and you'll see many families doing their Sunday thing. (The Piazza di Popolo was full of kids' teams playing soccer to loud music in front of ancient pillars and fountain.) After the Galleria, we walked to the Spanish Steps stopping for pizza and beer at La Pomodorino, a casual neighborhood eatery where we were the only ones who didn't speak Italian. We felt very Roman!
There are a number of galleries and museums open on Sunday, but some restaurants and shops are closed. If your wife is committed to that particular dish, by all means, search it out. I remember quite a discussion of cacao e pepe on TA. You can find reviews there and hours for a place near where you will be that day. While I planned ahead A LOT, listing restaurants and printing maps, we found the most memorable meals were the ones we stumbled upon. When we were tired and hungry, there was always something fabulous to eat nearby. Watch for happy people serving/eating food that looks good to you.
You'll enjoy the walks, and if you have downloaded Rick's app, you'll like having a guide in your ear so you can look around you instead of at the guide book. But take the maps from the guidebook! SO VALUABLE and clear. Have a good time!!
Ciao!
Polly