Saint-Germain and Morfontaine are special enough to compete with plenty of the other Paris attractions (sorry Luxembourg Gardens, catacombs, Pompidou, etc.). If you were in Paris for just three days, then maybe golf doesn't make sense. But you cannot see everything in one trip anyway, so why not take a little time for something you enjoy? Both of those courses are fantastic, and you also get to experience some different golf culture.
If neither of them works out, Fontainebleau is also well worth seeing and could be combined with a day trip to that chateau.