For my Northeast Corridor rides, coach is perfectly fine, and the fares on the Northeast Regional are high enough that the true "budget travelers" are going to be riding the Chinatown buses, anyway. That said, I definitely take business class if I'm riding overnight on 66/67, and during busy times, when the trains really get full. Even if Business class sells out, I have more room. I sometimes take business class just for the hell of it, because I can get the 25% AGR TQP bonus. I also ride business class on the Carolinian and Vermonter, and the Empire service, as the coaches are Amfleet 1s, and I appreciate the extra legrooom on a longer ride. I also ride Business class on the Palmetto, even though the coaches are Amfleet 2's and there no difference in legroom, because, in my experience, I've always had a seat row to myself in Palmetto Business class all the way from Savannah to Baltimore, whereas I've seen the coaches, and they fill up. At least on Saturdays in mid-April.
Generally the only time I spring for the Acela is when I have first class upgrade coupons to use. Now that is first class, with roomy seats, open bar, and meal service included. Actually, I'd use Acela anyway to go between Baltimore and Boston, because it does cut a whole hour off the trip compared to the Regional. The Acela first class crowd is more what you would expect of first class, the fancy business people and such, but not everybody is like that.