I think we tend to focus inordinately much on Air as the primary competition for Amtrak and also focus on relatively longer distance segments. Actually Amtrak has vast number of medium distance travelers even on LD trains and the primary competion more often is Cars than Air, by a rather large margin. Yet we seldom discuss either of those and discuss endlessly about how long distance Sleeper service competes with Air or not. Seems like a misdirected focus.
I used to travel to the Akron, Ohio area for work from Baltimore or Washington. It's about a 300 mile trip, and took me about 7 hours when you factor in meal stops and rest stops. I really would have liked to take the train, except, of course, the only train in the area stops in Cleveland, an hour away, in the middle of the night, so that doesn't work. But, just for kicks, I priced a trip for Dec. 15, 2 weeks from today. WAS-CLE, coach fare on the Capitol Limited was a Value ticket for $73. (Sleeper was $352, FWIW).
Now the cost of driving 300 miles, using the new IRS allowance of $0.625 per mile is $187.50. In addition, there's maybe $15-$20 worth of tolls, plus whatever meals you might eat on the road. If you make it an overnight trip, you have to also factor in the cost of a motel, which in most parts of the country is at least $100.
Clearly, it seems that taking the train is cheaper, at least if you don't have to rent a car at the destination. The Cap is a 10 hour trip, so you really don't need to book a sleeper, at least you wouldn't have to if they had a train on the route that would run during the day.
Another route I've taken is Washington the Charleston, SC on the Palmetto. About 450 miles., so operating a car would cost about $280. Coach on the Palmetto for Dec. 15 is $112, Business class is $168. [I should mention that I flew down to Charleston for a business trip last April, and the one-way fare was $350 (on Southwest Airlines, no less), plus a $50 Lyft to the airport and a $17 taxi to my offsite rental car location.] You could also do an overnight trip on the Silver Meteor, coach is the same, but a sleeper starts at $870. This economical coach fare certainly explains why whenever I've ridden to Palmetto north from Savannah there are always large crowds waiting to board at Charleston, Florence, Fayetteville, etc. The fact that driving I-95 through the Carolinas and Virginia is a miserable experience might also induce many people to be willing to pay a little more just to avoid having to drive their own car, or even a rental car. I have taken this trip to Hilton Head using all three modes of transportation (train, flying, and driving), and, believe me, tasking the train is the best way to go for this 450 mile trip.