Indeed. I could probably have put four of my 22" rollaboards in the overhead bin above my seat on the Acela I took a couple of weeks ago. (Well, probably not, but you get the idea.) Plus, there's the space at the end of the car Alan mentioned.

Unless you're moving your entire household belongings, there's never any need to be concerned with carrying on too much luggage on Amtrak.

Just so you know, though, Amtrak does offer checked baggage service between PHL and NYP. Acela itself doesn't have a baggage car, but if you do want to check your bags, you can do so in PHL and they'll ride up to NYP on the next train passing through with checked baggage service (could be an hour later or could be late at night, depending on when you're traveling). You can then return to NYP later to pick up your bags--actually, that can be a pretty convenient option (it serves as a free left luggage service if you're going to want to go around NYC and do some things without your bags before checking into your hotel).