I LOVE LOVE LOVE trains!
Many moons ago, I spent three months on a train traveling the country, and it was an absolutely wonderful experience. The trip, I kid you not, was incredibly cheap - I think in the neighborhood of $248 (round trip, and it allowed me to make a stop anywhere I wanted on their line, as long as the total trip was completed in 90 days or less).
I never got a sleeping car, preferring to save money by staying in the coach section. I did get off the train many times in my journey, and coordinated with a Hostel group to see where I could get "hotel" rooms to stay at along the way. Those rooms were about $10 per night.
The trains were very clean, comfortable, and the staff was very friendly.
All told, I had an awesome adventure, and would totally do it again if I could.