As I've pondered this topic. I've wondered how much the strength of the dollar relative to both the Euro and Pound has affected American tourism numbers? The answer to "over-tourism" seems to be to visit outside of high season (maybe even outside of shoulder season?) and visit places not on travel writers' recommended lists.
I like the idea of limiting number of visitors on any given day. It's good for limiting crowds at a sight but doesn't work for my travel style. I prefer flexibility. I'd rather miss a sight here and there than be tied to reservations I have to make months in advance. Last trip I did make a special effort to reserve a spot on a boat to Skellig Michael - only to have the boats not run because dock maintenance, on the island, hadn't been completed. Fortunately, I had a plan B on the chance that weather would keep the boats from running.
From New York Times:
https://www.nytimes.com/2019/08/29/travel/colorado-overtourism.html