We will stay in Menaggio on Lake Como for three nights with two days available for sightseeing. We will have a car. This is our first visit to Lake Como. Is there enough to see in the area to devote our two days to the lake? Or should we spend one day seeing the sights/taking a boat around the lake and drive to Switzerland the second day?
A bit of background: we are in our late 60's, tend to enjoy a more leisurely pace (not a check things off the list couple), love beautiful scenery. This will be our sixth trip to Europe.
Thanks.

Especially since you say you enjoy a more leisurely pace, I would say there is more to see/do on Lake Como than you can see/do in two days. (Of course, it depends on what's on your sightseeing list.)

You might want to study the ferry timetables to understand travel times. Scroll down the page to see spring 2016 timetables in pdf. If your trip is in summer, service will be slightly increased.

http://www.navigazionelaghi.it/eng/c_orari.asp

We are very active travelers, have been to Lake Como four times, once for two weeks without a car, and never have run out of things to see and do. Explore the lake by ferry. You will be located right in heart of the triangle ferry routes with the prettiest scenery on the lake. Go to Lenno and visit Villa Balbaniello. Bellagio and Varenna are a short ferry ride from Mennagio, explore them and their gardens by the lake's shoreline..
Villa Carlotta is near Menaggio. Walk the lakefront promenade in Mennagio.. Loads to keep you busy.

Lugano (Switzerland) is closer to Menaggio than Como. All depends on the places you want to see. For cog wheel railways and gondolas to viewpoints (4 lakes and Alps from Mont Blanc - Matterhorn up to Bernina - Ortles) you best go to Lake Lugano, for Swissminiatur, the Tamaro adventure park, the famous Riva San Vitale Battisterio or the copy of Leonardos Last Supper at Capriasca too. Other gems and botanical gardens are just around Lake Como.

Don't plan too much in advance and decide once you are in the area.

Since you will have a car, and will be on the "correct" side of the lake, it might be a bit easier to simply drive to both Villa Carlotta as well as to Lenno although you can do both by ferry if you'd rather.

Here's the link for the ferry schedule. Be aware that most of these are foot ferries although there are also some which accommodate vehicles.

Sorry, the link:

http://www.navlaghi.it/eng/c_illago.html