We've done auto train, but not the regular amtrak. We always get a sleeper car, DD goes to bed early 7:30 and I couldn't picture her falling asleep as everyone else was still chatting and other children were up and about.
It is not the cheapest way to travel, but we enjoy the train ride. And as someone else mentioned, we look at it as an adventure. Some train rides have been more of an adventure then others.
We have some friends that took amtrak from NYC in april, we drove in april(from NYC) we got there in less time then they did.