PHL-NYP is short enough of a run that I probably wouldn't bother to spring for F unless you were really interested in trying it out to see what it's like. The Acela first seats aren't really any better than the business seats, especially for a pair of people (the single seats are nice for single travelers, but they're only a tiny bit wider and don't feature any more pitch). And honestly, on that short of a run, seat comfort isn't a big deal--I'd probably just book Regional coach.

However, in F, you will get a pretty decent meal (on par with what you'd get in business class on a good airline) and complimentary alcoholic beverages. You'll also have access to the Club Acela in PHL (which also features elevators that take you straight down to the tracks, so you don't need to be board with the common masses when the train arrives) and another one after detraining in NYP (if you'd like a little place to relax before heading out into the city). If the price difference isn't an obstacle for you, it might be worth it just to enjoy those extra amenities.