Has anyone taken this trip? You can do the train/boat in one day or stay overnight in any of the towns (on your own dime) and carry on the next day. It does not seem expensive at 58SF. We would leave from Locarno.
In 2007 we did the trip, starting from Stresa, took the ferry to Locarno, spent half a day wandering, incl. the funicular, then took the train back to Stresa thru the Centrovalli and Domodossola. It was a glorious day, beautiful scenery. We spent a couple of hours in Domodossola, pretty historic centre in the town. Well worth the money! If you have time and the weather is cooperating, take the funicular up the hill in Stresa. Beautiful views of the surrounding areas.