Two problems: 1. The train is about triple the fare. 2. Vacations are so short that you have to minimize travel time. A really fast train should be able to make east coast / west coast in less than 24 hours, but we don't have those.
But, if I had to fantasize a train ride, it would be like this. Leave a little before dinner. Have dinner on the train. Read a book and go to sleep. Wake up -- have breakfast -- meet people, talk to people, have time to plan what to do when you get there. Get there midafternoon -- relaxed, rested, happy. Same on the return trip.
This would give people time to digest their vacation, to reflect on what happened and what didn't and what they would do differently next time.
As it is however, you have to hit the ground running in both directions after the fairly stressful experience of being many thousands of feet up in the air with no room to move.
Bother,
Joanna