Some people need weed.

[Razzle]

People who smoked in the 60s-80s are frequently amazed by how modern weed knocks their socks off. There is a HUGE difference between smoking 4% THC and 20%.

*I* smoked it in the 70's and 80's.  Frankly, what people are subjectively "frequently amazed" by isn't a good metric for determining the truth value of a claim, in my estimation.

Yes, 4% THC is weaker than 20% THC.  So what?  This kind of illogic would inform us that it's it's impossible to get just as drunk drinking beer as whiskey.

In terms of accessibility I think it was very comparable to where salvia is at the moment: legal, but you can't just wonder into any local bar, pub, corner shop or supermarket for it as you can with alcohol.

"I think" is also a poor metric for determining the veracity of claims.

TL;DR:  [citation needed]

Was probably more expensive, in relative terms, as well.

"Was probably".

You have anything beyond opinion on this matter?

Have you continued smoking between then and now, or have you tried it over the last 5 years after not having any since the 80s? Also, have you gained significant weight since then? Tolerance, the gradual nature of the potency increase, and increased body mass, are all likely to stop you noticing the difference. I was talking about people who suddenly try it now after not having any since their youth. 

And when we're talking about the appeal that any particular drug holds over other drugs to the majority of people, the quantity required to get you high does matter enormously. If all alcoholic beverages were as weak as shandies, yet cost the same as spirits (the average price of weed does not increase just because the average potency increases), alcohol would be much less popular, at least for the purposes of getting high. This is even more true of drugs that are smoked because many people who would happily smoke one or two, wouldn't have the patience to smoke their way through seven joints at once for the same effect. 

I have no clue where to look for information about the typical price of weed back then. I'm merely suggesting a possible explanation for why weed wasn't satisfactory to people, to counter your claim that what happened during prohibition is evidence that what I'm suggesting would not work today. I see no reason to assume, and many reasons to doubt, that the contexts are similar enough to draw such conclusions. I'm open to the possibility, but without more details, I'm unconvinced.

It seems highly probable that it would have been more expensive then because imported goods in general were more expensive, and combined with the lower quality (which would have been compounded by the longer time in transit) it seems reasonable to wonder how much more you'd have to spend to get reasonably high, compared with today.