Yes, Le Marais is a great vintage spot.
You have also :
Noir Kennedy : rock, rock, rock, so a lot of black and leather... 12, rue du Roi de Sicile, M° Saint Paul.
M'mzelle Swing : 36 , rue du Roi de Sicile, A real vintage boutique, the owner have an amazing 40' look . 50',60', a lot of dresses, gloves, hats .
Rag : 81, rue St Honoré M° Les Halles
Of course, you must have look on Didier Ludot , Haute Couture Vintage : coats made by Cristobal Balenciaga or "NewLook "dresses by Monsieur Dior....
Bon voyage !