Enough to do at Lake Orta for 2 nights?

One day is probably enough. We stayed there two days and had seen and done what we wanted.
You take a boat out to an island, walk around there and in the main village. We encountered terrible odors from a nearby paper plant which affected our impressions of Lake Orta. We wished we had visited it as a day trip from Lake Maggiore.

I also took the VI tour. We opted to stay a 2nd night at Lake Orta and really it was too much. If I had it to do again I would stay the AM, eat lunch there then have the guide arrange a taxi for afternoon to Milan. BTW, the guides start figuring out an exit strategy on about Day 3. Ours organized cabs for people to Malpensa and Central Milan. Even though we were leaving the day after the tour ended she organized a taxi for us and for the other couple who were also staying.

https://en.wikipedia.org/wiki/Sacro_Monte_di_Orta

By staying the extra morning you can walk the Sacra Monte, then have lunch on the piazza then head to Milan in Mid-afternoon if that works for getting to Varenna or perhaps you want to stay over in Milan/

My outlook could also have been colored because it was pouring buckets but I think we saw everything AND shopped, lol!!

This is a wonderful tour! Have a terrific time!

I spent three nights on my own at Lake Orta last summer, and would gladly have stayed more. I loved it. I walked all around the peninsula, up and down the Sacro Monte several times, hiked though the hills, found great restaurants and did not encounter any industrial smells.

If you do stay longer, I hope it's a weekend. There's an agriturismo not far from the train station that has the most unbelievably fabulous family-style meals on weekends. They bring you whatever they have cooked that day. In my case, that was 3 antipasti, 2 primi (pasta), 2 secondi (meat dishes) and a sampler of desserts. Plus wine. Sounds like just way too much, and it was, but the portions weren't huge and every bite was delicious. It's called Il Cucchiaio di Legno (The Wooden Spoon)