I'm guessing that all the "must-do's" means the 3-star sites on Rick's At a Glance list. But what about all of the 2-star sites? This list doesn't even mention walking tours, photo safaris, river boats, other churches covered in the book, including the royal tombs at St. Denis, flea markets, food markets, or more Chateaux near Paris. I'm another one who has made several visits and would return at the drop of a hat.
Also, it's cheaper to book ahead for your TGV from Paris to Switzerland (or to Dijon or other destination), but booking ahead for a train to immediately follow your flight arrival could result in you losing the price paid and having to buy a new ticket if you miss the connection.
I generally believe in flying as close as possible to the first place were you want to spend time. Flights to Paris can usually extend to a connection to Strasbourg or Basel/Mulhouse airports for about the same price, and hopefully all on one ticket, so that the connection is coordinated.