Rebuilding Notre Dame will provide work. Its not entirely useless, and those workers will spend a bunch of their pay which will in turn have a slight stimulus effect so that it be as if more than 100 million was used. This also may stimulate a little extra tourism, so there are some benefits to rebuilding.
I think they should not completely restore the building and instead should make it into a mixed modern-ancient building used as a museum. The fire is part of its History, and it shouldn't look exactly like it did before. Instead of recreating the old roof they should put in a nice glass roof (or something else), and they should take the old burned stones and make some cool stuff out of it.
They could auction some of the stones and donate the proceeds to charities.