Portofino is my favorite.
You already have Mama Della on the list and that is definitely a dont miss. Request Joe to be your waiter, he is awesome. Sal's for a slice or a panini is great too you can even have it sent to your room. The ice cream place thats attached, The Gelateria Caffé is excellent. My kids love the gelato and I love the cappuccinos. In the AM if you dont want a full breakfast you can always grab some breakfast items there as well.
My kids love to throw coins in the fountain in the lobby. I like to shop in the gift shop off the lobby.
In the evening be sure to take the boat ride from citywalk back to Portofino, its beautiful.

Also when you get back have a cocktail at The Thirsty Fish and sit on the Piazza. Take pictures on the Vespas.
Be sure to visit the Art Gallery next to Sal's. They have some amazing and very interesting pieces. I have been collecting Frogs from the Frogman from this gallery for years.

Visit the Villa pool and jump in the cold plunge pool and then the big pool - my kids seem to love to do that.

After, relax in the hot-tub that at the villa pool its usually empty.
Grab lunch at the beach pool one afternoon. Maybe rent a Cabana. We like to get a cabana at Hard Rock though. The Beach Pool slide is lots of fun and there is a hot tub hidden up behind the rocks.
Take in all the trompe l'oeil on each of the buildings - very cool and I still love looking at it 10 years later.
We enjoy having a full breakfast or the buffet from Trattoria del Porto outside on The Piazza at least one morning during the trip. The food is great and the service is excellent.
Usually at dusk dont miss Musica della Notte. The schedule changes so ask at the desk. When we were there is took place each evening. I found this description on their site.
Come and experience our daily show "Musica della Notte" (Music of the Night)! Each night at sunset Loews Portofino Bay Hotel's Harbor Piazza will come alive with a musical celebration that captures the romance and charm of Italy and the allure of Mediterranean hospitality.
Musica della Notte showcases a unique blend of classic opera, romantic and festive music, along with 'popera' favorites - the wildly popular musical style that bridges the gap between pop and opera. Three themed shows will be offered on a rotating basis Romantico Night, Classico Night, and Italian Festival Night.
Check out a Dive-In movie, usually at the beach pool one or two nights a week.
Divertiti!
Have a great vacation! Hope you enjoy Portofino as much as we do.
Ciao