For yowza factor with the Eiffel Tower twinkling above you though the glass roof, Les Ombres would be a good anniversary choice. The menu for dinner is about 70 and then add drinks onto that. We had a good meal there and the view is great.
A cozy wonderful restaurant near the Tuilleries is La Cordonnerie; tiny one chef place. If you go definitley get their grilled foie gras with cocoa.
Another place we love for celebrations is le Cottage Marcadet near the Lamarck Caulaincourt metro; you can see photos of our meal there at: http://janettravels.wordpress.com/2010/06/09/dining-out-three-experiences/
I would not get a tour of the Louvre unless touring is really your preference for museum visits. Evenings are less crowded but the light is also not great in some galleries and there will be large sections closed; closed sections are listed in the area near the information desk under the pyramid.
We like to do our own walking tours using maps and guides in various walking tour books or on line or just striking out for an interesting sounding church or a local concert (free musical events are listed in each week's Pariscope) and then exploring what is in the area -- or heading to the end of the line of a metro and finding out what is there. We once discovered the Island of Grand Jatte from Seurat's famous painting that way. You can see examples in the photo journal in the 'Paris' category of some of our walks.