We went to Walt Disney World for the first time in June 1974. It is STILL my favorite trip that my immediate family went on. The day before, we visited Six Gun Territory in Ocala. Though I was only 7 years old, I remember it all very well. It was soooooooooo hot during that vacation. I bet the temps were close to 100. There were lines but you could easily ride everything multiple times. It was pretty much like that well into the 1980s. The food at the Magic Kingdom used to be SO much better too.
I cannot speak for Disneyland but I know WDW, you can spend a 9-12 hour day and barely do one round of rides. I last went 12 years ago and we did not even bother with Space Mountain the lines were so long. The food was terrible. But I must say.....Even though it was not the best trip in the world 12 years ago, it still brought back great memories from 1974. Being that all of my immediate family is gone, it's even more special.
12 years since my last trip, the lines are worse than ever. My Wife and I REALLY want to go but it simply is not worth the cost anymore.