Is Lake Como worth it?

Sure, and it's a popular day-trip option. From Milano Centrale you can be in Varenna (Varenna-Esino station) in about an hour, kick around town (it's pretty), take a ferry to/from Bellagio or maybe one of the other towns, and get back on a train.

Is it "worth it" for you? That's a decision only you can make, and you do not have to make it until you're in Milan. If by Monday you think you've seen everything you wanted to, then get on a train. Raining? Stay in Milan.

Bergamo is another nice day trip, although not on the lake, It takes an hour to a little under by train, depending on what train you take, and the old part - Città Alta - overlooking the more modern city is deliciously Medieval, if you like that sort of thing (I do).

Is Lake Como worth it?

yes

Yup, very worthwhile...and many others think the same. You're in Milan three nights, so I'd definitely choose Lake Como over one of those days in Milan....and I like Milan.

Oh my, yes! Go early. Get on the train to Como. Grab a taxi to the lake (lago). Buy a ticket for the hydrofoil to Bellagio. The boat trip lets you see the towns around the lake and the Alps. Lake Como is extraordinary. Bellagio is stupendous. Walk UP alleyway, come down a different route. Eat, shop, stand at the lake and stare. Just keep your train timetable in mind. It will be memorable, even if your day is damp. Ooo--jealous :D

Is lake Como worth it?

Every penny of it.

Are you buying the whole lake?

Definitely worth a day trip from Milan
YES

That said I was not as fond of Lake Como as I am of other areas, but that is of the mindset of it as a place to stay for multiple nights. Lakes never impress me as much as oceans can. If you are in Milan and could see it as a day trip, definitely worth doing.

It is definitely worth it. I would spend one night in Varenna . Varenna is not very big so you can easily see it in one day. You could also ferry to another town. If you decide not to spend the night, it would still be worth it. Just remember to buy a round trip ticket and validate it. You probably won’t be able to buy a return ticket at Varenna’s train station. In 2015, they didn’t sell tickets at Varenna train station.

You don't say if you're arriving from the US on Saturday. If yes, and you are leaving on Tuesday, you'll probably be a jet-lagged and I'd suggest you stay in Milan and see all it has to offer. The weather is likely to be nice in early September ... take a walking tour, visit the Duomo roof, get tickets for the Last Supper, follow Rick's walking tours ... There is more than enough to keep you entranced for two full days (Sunday and Monday.)

If jet-lag is not a problem and the weather is perfect, here is what my wife and I did in October. The 10am train from Milan Central to Varenna ... tour Varenna for 1 1/2 hours ... 12:30 ferry to Bellagio ... tour and lunch in Bellagio ... 3:30'ish slow ferry to Como, enjoying the sights and little towns along the way ... walking tour of Como's older section with an aperol spritz break ... 7pm'ish train back to Cadorna station ... back to our apartment to drop our day packs ... 8:30'ish dinner. An absolutely perfect day! Perfect weather, perfect pace, beautiful sights. Not in-depth ... more of a tasting menu, which sounds consistent with the amount of time you will have available.

We also visited Bergamo, and although it was a fun day and the town is beautiful, it doesn't compare to the incredible grandeur you will experience on and around Lake Como and its towns.

We also visited Bergamo, and although it was a fun day and the town is
beautiful, it doesn't compare to the incredible grandeur you will
experience on and around Lake Como and its towns.

It was pretty foggy on the lake the day we did Como (from pretty Varenna) so I'll have to go with Bergamo just because we had better weather there.