I started attending Lehigh University in Bethlehem PA in 1967 and thus had several opportunities to sample travel on the NEC between Philadelphia/NY and my home near Boston.
This was during the dreaded Penn Central era and I would say although interesting from a railfan standpoint, as a practical means of travel I don't believe the NEC was viewed as favorably as the current Amtrak incarnation. Trains weren't even on most people's radar, and with air fares relatively cheap (if you were lucky you could get a $9 standby ticket on Eastern Airlines from Newark to Boston). Although I would say the trains were generally well patronized, especially on holiday periods, although not like they are today.
There was a great deal of deferred maintenance. For example my first trip home Thanksgiving eve 1968 I rode in an ex NHRR Stainless Steel coach with lights that went out at every stop - most likely dead batteries. The lights failed completely after NY. Then there were the P70 coaches on the NY to philly clockers (as noted by Mr. Norman), which were on their last legs. Many of the cars were not clean, and a trip to the bathroom could be an adventure. Timekeeping was often affected by the maintenance issues - stuck drawbridges, derailments, etc.
There were other compensations, especially for the railfan. Some trains still had real dining cars, although whether the commissary had gotten around to provisioning them was hit and miss (one such trip out of Boston had already run out of eggs by Providence so it was OJ and toast). You also saw mail trains with RPO's and long Florida bound trains of sleepers with exotic name boards (for this New Englander) such as SCL and RF&P.
Another inconvenience that was resolved by the Amtrak takeover was that many Boston - NY trains terminated at Grand Central so that required a long walk or a trip on the subway to continue one's trip south from Penn Station. The subway in NY is another institution that has come a long way since those days
There were 2 bright spots, the Metroliner and Turbo Trains. I did have the opportunity to ride the latter which was quite an experience.