I don't know if its worth it or not. Ive taken 66/67 about a dozen times over the past year and my experiences are mixed. On 67 (the southbound), I usually take coach as I usually get a "two side" to myself through New York and usually to at least Philadelphia. At Philadelphia you pick up a fair number of business types who are going to DC and my experience is that the train is at least 60 to 70 percent full. Going to Boston, there is only one "major" stop after New York (Providence) and I find the chances of having to share a seat on train 66 to be lower.
As to business class, I've opted for it twice. Both last minute because the demand was so low that the difference between what I had paid for coach and the offered business fare was so small, that it was worth it to me. One time, I booked WAS to NLC for $133 and about an hour before departure time, business was $150. Easy call there.
As to consist, its hit and miss. I agree with hi55us. The only insight I've had into guessing in advance as to what the consist would be would be to look at business class availability one to three days before departure. If business is close to sold out or has "one seat left" or "two seats left", chances are its a leather seated business car (combi business-cafe-coach table car). 66/67 rarely have enough passengers for a dedicated business car.
Now all that said, on my last 67 trip, I talked to conductor who mentioned that there are discussions regarding re-introducing a sleeper service on 66/67 - provided more Viewliner II sleepers get delivered.