Great trip report Seat 2A.
I took my first long distance trips in the US earlier this year having previously traveled all over Europe by train without bothering with sleeping compartment or couchettes. Many of the trains had seats divided into compartments that pulled down to make one big bed that would be shared by whatever backpackers were overnighting on that trip. I remember one funny train ride from Venice to Nice that at 5am in the morning changed from a quiet journey through the night into a commuter train, guys in suits with briefcases burst into the compartment and pushed all the seats back into the regular sitting configuration, toppling myself and a fellow (female) backpacker onto the floor in a severe state of undress!.
During the summer I took two long Amtrak rides:
The first was from DC to Miami and back (small train, no view, poor service, deluxe sleeping compartment which I would definitely recommend for the extra money as you get a much larger bed, more space, views to both sides of the train, and a private shower).
The second was cross-country from DC to San Francisco (both times changing at Chicago). Outbound was on the Southwest Chief, Chicago-Los Angeles (excellent service and food, great scenery, same kind of two level train as the coast starlight, upstairs rooms have much better views than downstairs). I was supposed to change from the Chief to the Coast Starlight in LA but due to the Chief running more than a few hours late we had to swith to a bus and ended up chasing the chief half way up the coast missing much of the best scenery.
The return to Chicago was on the California Zephyr which was the highlight of the trip, the scenery was amazing leaving California via the Donner Pass, heading through Nevada in a sandstorm, through Utah then spending the best part of a day winding through the rockies. Apart from a 30-minute break in Chicago I was on a train non-stop from 9am on Tuesday (Emeryville, CA) to 4pm on Friday (DC).
I expected to read a lot of books and watch a lot of DVDs but I spent most of my time just staring out of the window.
As you mentioned, the dining cars can get very crowded, the best way to avoid the wait is to go for the earliest dinner sitting or to ask your sleeping car attendant to bring your choice of meal to your sleeping compartment.
I would definitely recommend Amtrak to people who want to do nothing for a couple of days and just watch the world go past, and I am going back on the Zephyr soon to see the snow through the Sierras and the Rockies.