I live in DC and go to NY a couple times a year, for a decade+. It can be a little faster to fly, sometimes it can be a little cheaper (but that depends a lot on when you book), but AmTrak wastes less of my time. Living in DC proper, it's faster for me to get to Union Station. Once there, maybe I'll grab a coffee and then it's time to board the train. I get on, I sit down, I plug in, and I have three hours of no hassle quiet work time. Then I come into Penn Station, catch the A train downtown, and I'm at the NY office. There's way less standing in line, dealing with security, being shutdown due to taxiing, waiting in traffic, etc.

The Acela is useful if I'm trying to make a tight time window. However, I prefer the café car booths on the Regional.