Maybe not a private car, but I treated my wife to a full bedroom on the e/b Lake Shore Limited night before last, her first experience of any kind of sleeper accommodations. We're planning my (early) retirement this year, and according to her I think we'll be doing this again... and again, and again.
Funny part about it is that we had coach tickets, but on a whim, while on our connecting train I checked online and they had Roomettes and Bedrooms available, and I said to myself "Why not?". It was a damn good thing I had the impulse to do that - Spring Break Friday. The train was absolutely packed to the overhead racks with college kids, not a seat to spare. We had planned to sleep in our coach seats. Wow.