Seats are something tangible we can debate, but I don't think that should be a limiting factor to comfort. Having ridden in the Illinois Venture cars, I found the seats to be generally fine - not great, not terrible - but far more important, the smooth and quiet ride of the cars is a huge upgrade and would be a critical change for overnight travel. Likewise, the sliding plexiglass doors that open and close virtually silently, as opposed to metal doors slamming shut.
I am 100% in support of a lie-flat product - I'm not spending the absurd money on a roomette anytime soon. That said, Amtrak needs some significant cultural changes to support a lie-flat or overnight business class product. I do not see any will from current on-board personnel to enforce (theoretical) quiet hours, require the use of headphones for movies/music, cut off endless phone conversations, etc. I've literally watched Amtrak personnel walk right past these situations in coach and do nothing; I know if I'm traveling on an airplane, I can usually expect flight attendants to address these situations.
As someone who used the Lake Shore Limited business class product, Amtrak struggled to correctly turn the half-cafe, half-business cars so that the business section was not subject to the non-stop foot traffic to the cafe. I would be hard-pressed to say that anyone at Amtrak's management level really cared about creating an actual business class "product."