Apart from Australia's UA, Appeal is mainly used for National Parks and Seaside Resorts.
National Parks must have all tiles with Charming appeal or better. The tourism it generates is equal to the appeal of all tiles in the park (so a National Park with 3 tiles with 4 appeal and 1 tile with 3 appeal would produce 15 tourism).
Seaside Resorts need a coastal tile with at least Breathtaking appeal. The generated tourism is double the appeal of the tile, and the generated gold is equal to the tile's appeal.
The Eiffel Tower works exactly as it says: +2 appeal to every tile in your empire, regardless of city. It's enough to kick up Average tiles to Charming to Breathtaking.
The Great Engineers give the bonus only on those tiles of a particular city (regardless of being worked or not), as seen on the "Manage Citizens" screen.
Don't underestimate the tourism kick from Resorts and Parks, since they can be built almost everywhere if you plan it right. Every Resort gives at least 8 tourism, and every park at least 2 tourism per tile (total of 8 tourism), not counting the Computer tech. A few of them is equivalent to a themed Museum.
Combine Eiffel Tower with Cristo Redentor for even better results. Cristo doubles tourism from Resorts, Eiffel Tower kicks up appeal a notch to boost your existing Resorts and allow to build even more of them.