The point of offering sleeper service on Amtrak isn't to make it cheap, it's to allow Amtrak to soak up some extra financial gravy to help their revenue bottom line. If passengers want cheap, they can ride in very roomy reclining coach seats. The challenge for Amtrak is to figure out a combination of fares and service levels for the sleepers that will maximize their net revenue. If the service level costs too much and the fares are too low, then net revenue is not maximized. If fares are too high and the service sucks (hi, flex dining!), then they may lose customers, but it's possible net revenue would not be impacted as badly.
Having ridden 66/67 overnight in business class many times, I can say that the only thing I'd want from a sleeper is the ability for lie-flat sleeping. The only other on-board service I've ever used was getting a nightcap in the lounge car. Train 67 leaves Boston at about 9:30 and gets into Washington at about 7:00 the next morning. No need for breakfast, you can get that in the station. When I rode it, I used to go right to the office and get a shower downstairs in the fitness center. It would be entirely reasonable to offer lower Washington-Boston sleeper fares on the basis that there's no included meal service. Actually, keep the service level minimal the whole way, and have cheap(er) sleeper fares for the whole run from Newport News to Boston.