Hello Christopher:
Well it seems as if you've got no shortage of responses. Good.
I was 14 in 1980, about the time I started journeying about on my own to a large extent. My earliest memories are of the Q's (one ride as a small kid) and plenty of R9s, and the old B&O SIRT, but I think I missed the ABs. I recall the East 105th Street grade crossing, but like you, missed the Third Ave El (I'm from Queens). So I recall brand new R-44s clearly, also some upholstered seats on the IRT and plenty of green and red trains of all sorts.
Well cleanliness and comfort were not as good in the 1970s as today. Air conditioning was rare, except on R-44/46 types where it seemed fairly reliable. The axiflow fans and openable windows were OK, but inadequate. Yes the sensory experience was there - the ozone smell, the noise, etc. - but for the commuter, the experience was like roulette - you never knew what to expect. Graffiti covered everything, including maps and windows, and cars were washed less frequently. There was a real sense of disorder and fear; crime was worse then, too.
Maintenance was terrible; slow orders were everywhere and breakdowns were constant. A good portion of the fleet was out of service (R-44, R-46, R-16) due to maintenance issues (and cracked trucks on the 46's). So there was a terrible car shortage, dropped trips, etc.
So yes there was nostalgia - incandescant stations, maybe faster top speeds and so forth - and the TA was a little friendlier to fans (plenty of fantrips and open houses around the Diamond Jubilee in 1979) but the quality of service was worse and there seemed little hope that it would get better.
Metro-North (then Conrail and Penn Central) was my favorite. No two coaches or locomotives seemed alike, they even ran an S-motor in GCT until 1980 or so. They've done a remarkable job turning that service around in the past 20 years. But I miss the RDC's with the end doors open in the summer!
FYI, when I could, I spent time in Philadelphia in my teen years. I rode all sorts of stuff there - PCCs on long-gone routes like the 50, Red Arrow 80 cars, the old Broad Street cars, the P&W Bullets and Straffords, Reading Terminal - Philly was a true railfan's paradise then, a rolling museum. I miss the GG1s too......
Cherish your memories now, because they will become the nostalgia for the next generation! Take pictures too, but don't get carried away with them. Too expensive.
CONRAD MISEK