In terms of Boston to NYC, the NE Regional is usually the better value than the Acela. Acela truly shines when it's more "long haul" like Boston to Philly/Baltimore/DC.

I 100% feel NER business class is worth the upgrade over coach. You get an assigned seat and complimentary non-alcoholic beverages. You can bring your own non-alcoholic drinks and food on the train as well.

As for booking, it's recommended to book at least 14 days in advance to save money. Cost can swing wildly like airlines so be prepared for that.

The big plus with train travel is that there is far less security theatre and 2 free "checked" bags. When I go to NYC, I don't have to bother going downtown to Logan either. I live in the burbs and park at the Westwood/Rt 128 stop which is so much cheaper than Logan.