I would agree that it is time to get rid of the Amfleet cars if there weren't potential corridors like new ones in Ohio, the Northeast and Midwest that could be started or expanded. And its not like the Republicans will budget more than enough to replace the Amfleet cars, a small increase in fleet size would be a minor miracle knowing them. Trump might be convinced to go along with a larger car order, but given how the Democrats are treating the shutdown and how anti spending some Republicans are, a larger order is tall order.
My understanding is despite any specific size quoted, the goal of Amtrak is really to setup a pipeline of 100-125 cars a year for 5 or more years. The idea being to give constant work for awhile, not just one big blip in orders.
If this does occur, then ideally states can add on in later years for more captive equipment, or Amtrak can expand the order down the road.