I have traveled in both coach and in a sleeper on Amtrak's AutoTrain so I thought I would provide some detailed information here. While very small, the roomette I have booked seats two people very comfortably. It is quiet (except for the train noise, of course) and private. When we return from dinner, the seats have been converted into upper and lower berths where we can sleep flat, with a nice pillow and blanket.
The meals and service in the sleeper dining room are superior to what is available in the coach dining room. For a 4:00 p.m. departure, boarding is at 2:30 p.m. and there is wine tasting and snacks available in the lounge car.
But here's the real kicker! Think that roomette is going to cost you a small fortune over the cost of coach? WRONG! I recently had to book an AutoTrain trip. Clicking around my keyboard in a hurry, I was mortified at the cost of the trip but resigned myself to it. Several days later, when I actually planned on booking the tickets, I was amazed at the lower price.
Then I realized, when I had checked a few days before, I had forgotten to click on the roomette link and had actually originally priced out coach seats. Just to double check, I ran the numbers again...same day...two passengers, one vehicle...two coach seats versus a roomette. Amazingly enough the roomette was actually $75 (total) cheaper than buying the two coach seats!
So if you'll be traveling on AutoTrain, don't hesitate to check the cost of the sleeper. You might be pleasantly surprised.
(Note: Amtrak offers discounts to AAA members. If you are booking AutoTrain and are not AAA members, you might want to think about joining. Your cost of membership will probably be paid for by your train fare savings.)
(See also my February 2009 Auto Train and November 2010 Auto Train posts.)