First, 90 minutes is not long enough to see anything. I would walk through the station, grab a snack, then relax in the lounge. As far as missed connections, flying or rail, I find using the phone much more efficient and definitely cuts the lines. If the Amtrak phone agent has issues, I don't hesitate suggesting a supervisor reminding them that this is time sensitive.
Would have to agree here. After arriving getting off the train and checking/receiving your bags you have only a 90 minute window. You will board your regional train about 10-15 minutes early. You will have maybe 1:15 and that assumes an OTA. WAS Union Station has a huge food court, two Starbucks and a shopping mall within. If you were a sleeper passenger.You can wait in the Acela lounge I would recommend staying in the station. Too little time to get bored.