Peru does this on the Inca Trail trips. There is a daily cap on the number of people allowed on trail (tourist + guides + porters/cooks), plus guides are required. While it certainly isn't cheap, it wasn't prohibitively expensive (i.e., if you can afford the airfare and hotels in a city, you can likely afford to hike the Inca Trail).

Having recently visited Iceland, I could see that the Reykjavik-area was near its limits. As was the airport (gate areas were overcrowded throughout the terminal). There's plenty of space elsewhere on the island, but the government and Iceland Air have done a really good job convincing tourists to do a quick stopover en route from the Americans to Europe.

And being a regular visitor to Scotland (Scottish by birth, though raised in the US), there are more and more tourists every time I go back. Skye is running into problems supporting the number of visitors at peak season - many showing up without planned accommodation, camping on roadside, etc. The NC500 route is similar - the area is desolate and lightly populated, but it's been pitched as a tourist destination - great to get people out of Edinburg, but facilities are barely adequate, at least at peak season.