I forgot to mention that while we were staying in Curitiba we did the Serra Verde Express train to Morretes, and back again. I guess I forgot because it just wasn't that memorable.
We felt the experience to be quite pricey, with not enough to be experienced. The forest is so dense (which can be nice) that mostly you couldn't see anything. When views briefly became available you had to choose between looking or taking a photo, there wasn't time for both.
The town of Morretes is a pleasant colonial town, but H and I get out of the cities and into the country towns a lot, so it wasn't exceptional for us.
What we did like best was our lunch in Morretes. We went and had the barreado, which is a kind of slow cooked meat stew, served with banana. It was delicious.
If you were bored in your travels and had to fill a day, the Serra Verde Express is okay... But there are more interesting days to be had.