I was there opening weekend of Indy, and it was pretty fun, but nothing uber spectacular. There was a small jazz band playing classic swing numbers and taking requests on the roof of the Jungle Cruise building, so that was fun. The line was a couple of hours, not too bad, the ride itself looked great except the cars were so jerky you literally felt like you were going to get thrown out (it was scary! seriously!) and there were no seatbelts. Plus they had that annoying AT&T ad over the exit, but somewhere I do have one of those code cards stashed in my stuff so that was cool.
I'd go back to somewhere in the 1960s when Tomorrowland was at its zenith, Walt roamed the park, and people still had common sense & manners. And yeah, I'd just sit and listen to him talk about his ideas too...
And witness one moment of disneyland history, when/where would you go?
The first day of Pirates. Would love to see the reactions of the riders afterwards, to something they hadn't seen or contemplated before.
Other than THE Opening Day itself, most of the other rides aren't big leaps conceptually from what folks were acquainted with at the time. I think Pirates was a big leap for those lucky first visitors.