Sorry I didn't see this thread sooner.

ADVANTAGES

Long-distance train travel is much easier on kids than driving. Kids don't appreciate scenery, and they hate being confined to car seats for long periods. On a train they can move around and meet other kids.

Because the train keeps going 24 hours a day, you get where you're going much sooner than driving (assuming you're going cross-country).

Amtrak is much more liberal about luggage than airlines are. I've traveled with my wife and son and a complete set of camping gear: tent, sleeping bags, cooler, clothes, and cooking gear.

The local Amtrak station even allowed me to park my car in their lot free for the entire 2 weeks we were gone! (This might not work everywhere.)

DISADVANTAGES

Schedules are limited. The Empire Builder, for example, only travels once per day each direction.

In most cities, you can't just pop into a station any time you like and ask questions. The station might open only an hour or so before a train is scheduled to arrive, and close soon after the train leaves. It's best to get your information from the Amtrak web site.

You might find that your train is passing though the prettiest scenery at night, when you can't see anything! For best scenery watching, travel in June when the days are long.

In Minneapolis/St. Paul, they idiotically built the train station, the airport, and the inter-city bus (coach) stations miles apart from one another. You can take city buses between them, but of course, it adds to the trouble. (Not like in England, where the trains and the coaches go right into the airport!) Car-rental services might have a shuttle bus that will pick you up/drop you off at the train station, but you'd best inquire.

Trains can be crowded at peak times. I'd say avoid July and August and the last half of December. Traveling off-peak gives you more room to stretch out.

QUESTION
I'd like to hear from anyone who has tried to play an instrument on board a train. I think a folk jam in the bar car would be a great idea, but the management might not see it that way. I once met a bagpiper who tried to play his pipes (we were a bit drunk at the time) and was promptly and firmly told "You can't do that here." Several passengers were disappointed.