Where to from Menaggio (Lake Como)?

How about Lake Maggiore? Stresa, Baveno, Verbania are good bases and it's perfect for 3 nights/2 full days. Different enough from Lake Como to be complementary.

Or Turin. Great city.

Since you have a car, Stresa on lake Maggiore would be my suggestion. The drive from Stresa to Malpensa is about 50+ minutes, so take that into consideration if you return your car on the day of flight departure rather than spending the night at an airport hotel.

You might even consider Arona or Angera, still on the lake but more to the south therefore 15 min closer to the airport, but if you intend to visit the Borromeo islands, then Stresa is better, because I don’t think they have a lot of boat service to the islands from the other two places.

If you're looking to stay no more than a few hours from Malpensa airport, and prefer to stay to the west/southwest of Lake Como, one option could be to explore the Ligurian coast. Places like Genoa, Portofino, and Cinque Terre are within driving distance and offer beautiful coastal scenery and delicious seafood. Alternatively, you could head to the Piedmont region and explore the wine country, with towns like Asti, Alba, and Barolo offering beautiful landscapes and excellent wine tasting opportunities. Without a car, you could also consider heading to the beautiful city of Turin, which is just over an hour away by train from Milan and offers a rich history, beautiful architecture, and delicious food.

Thank you all for your feedback and suggestions. We found a wonderful agriturismo/spa in the Monferrato area only an hour or so from Malpensa. Many things to do and places to see as well as wine tastings in the Piedmont region.