If there are two of you may I suggest you take a taxi into Paris; it is a little more expensive but less hectic and you dont spend so much time underground. You can ask the taxi to take you around champs elysee, make a quick stop at the Trocadero (as mentioned above), drive through ile de la cite (Notre Dame) and then drop you off in St. Germain area; there are tons of restaurants and places to eat. I can recommend a couple if you like.
Once done, take a taxi back to CDG.