I have to agree that, with only a weekend, Versailles would not be my choice of where to spend a day. And, unless you really want to go to the top, you can see the tower from a lot of other "sites". Take the Metro to the Arc d'Triomphe, then walk down the Champs d'Elysee to the Trocadero in the evening and you cross a lot of the major tourist stuff off in one hour (or more if you stop, which you will.)
I think most of the touristy sites are good for one thing, congregating the masses and keeping them away from the really good stuff. There are exceptions, like the Louvre, but even there the Mona Lisa draws the crowds and you can walk some of the rooms almost alone. So, that being said, what do you like? Because the Louvre, the Invalides, the d'Orsay are all fantastic, and any one of those can easily take up a day or two on their own. The Petite Palace, the Musee Marmottan, or Palace Royal get a lot less traffic and are world class too. And seriously, you want to just walk; along the Seine, through the parks, even just in the neighborhood you find a hotel in.
Do you really want to spend your very short time in Paris waiting to be one of the 15,000 people a day being shoved through the Notre Dame? Or jammed into Shakespeare and Co. (when there are half a dozen bookstores within half a mile where you can actually browse)?
If you're going this coming weekend be advised it's going to be hot, without AC, and crowded. Find something to do inside in the morning, take a siesta, and plan on your evening meal around 7:30-8:00 pm. And frankly, if you don't already have tickets, your choices will be limited.