I, too, began flying regularly about 1983. The programs were established, although still fairly new. What seems astounding now looking back to the early days of the ff programs is how generous the awards were. On Northwest, you turned in coupons for each flight... one for coach and two for first. When you finished the book of 20 coupons you got an award certificate. That certificate entitled you to one free domestic coach flight, or you could save it and combine certificates for first class or international travel. It was, in effect, a "segment" system. How about that! Additional "perks" came with the certificate as well, including, as I recall, two or three nights at such hotels as Mandarin Oriental. Early on I had enough of these hotel awards and airline certificates for two of us to go to Hong Kong business class and stay a week at the Mandarin Oriental. Both the airline and hotel awards added up fast. Of course, that's why they couldn't stay so generous. You also got a week car rental, and some other partner rewards.
On many flights, first class was not a huge additional outlay. I remember "upgrading" some flights for as little as $20 ow.