Yea, not easy to get to. I saw them while on road trips just from driving. While I was in Oregon for my sisters wedding, I googled places to see while there and Thor's Well popped up and HAD to see it. It wasn't as spectacular as the above picture because it was a calm day and evidently not the season.
Yea, if you drop into 90 mins range those places are all must see IMHO.
All that said, I'd likely never really plan a vacation to go to one, not enough other things to do.
Then again I consider the French Quarter and old Yankee stadium far more iconic American destinations than anything on the list. (Boston Garden, Madison Square Garden, Disney World, Carnegie Hall, Busch Gardens, Vegas, Grand Canyon)
And those types of places offer a full itinerary.
I work for a company that is international and the folks who visit want to talk about those places not the aforementioned list.
Those places on the list probably rank higher once there but far less well known.
But if I had just finished reading Walden, I could see myself doing a commune with nature trip and loving that list.