I think there is no question that today's stuff is far better than the average stuff from the 1970s, which was effectively untrimmed seeded tops with stems, fan leaves, etc, that may not have been harvested at peak nor cured ideally.
But even in the '70s the best stuff was hard to find, and cost real money, and most people weren't smoking that, let along high-school teenagers.
If you could even get your hands on Panama Red (and you probably couldn't), you'd expect to pay several times as much for it as for "ordinary" weed. Good story here, by the way:
http://tinyurl.com/7ohqrmb
To the extent that there is any question here, I don't think its whether the average manicured indoor grown commercial stuff from today is way better than the typically seeded schwagg from 40 years ago (it definitely is). The question is whether or not the BEST outdoor grown pot from the 1970s is comparable to the best stuff from today.
Specifically we're talking about the Panama Reds, the Columbian Golds (not Acapulco), and some of the more "exotic" stuff like "Chocolate" Thai, etc.
Now, I wasn't smoking in the 1970s (though unlike some who post here, I was actually alive then), but my understanding is that the best of the older stuff actually does still hold up.
As mentioned, though, its a question of growing the right strains outdoors, in the climates that the strains have been acclimated to (typically mountains for the best stuff), over very long growing seasons. These "landrace" or heirloom strains pretty much have to be grown in their natural climates to get the most out of them.
Also, its been claimed that SEEDED pot is actually better than unseeded. The unseeded stuff will definitely give you higher bud yield per plant, and it may even be a little bit more potent, but supposedly the seeded stuff expresses different ratios of cannabnoids, and the QUALITY of the effect is better.