Parc Asterix is much more charming and fun than Magic Mountain. If you happen to be a fan of the comic (I sure am), you'll love the details. It's not Disneyland, but it's 1000% more themed than Magic Mountain. A couple of world-class coasters among the mix, too.
(EDIT) ...but stay off Goudurix.
Frankly, there is enough to do and see in Paris to eat up 2 whole days. Look into shows, nightlife, tours, museums, etc... Some really interesting things around the city, outside of the standards stuff. Lots of history.
A good place to look for simple day trip ideas is to go to Travel by Disney. Not that you should use their services (not that you shouldn't, but they are...pricey)...but, they have itineraries, etc., that make it easy to get an idea on what they consider possible with day trips, departing from DLP, and you can use that as a starting point for your own ideas / plans.
Anyhow, I'm out of ideas, but good luck! I'm sure you'll have an amazing trip!
I could spend a month in Paris and not have enough time to see everything I want to! Tour Eiffel, Arc de Triomphe, Champs Elysées, a boat tour on the Seine, walking along the Seine to shop with the "bouquinistes", musée du Louvre, musée d'Orsay, musée Rodin, musée Jacquemart-Andre, Sacré-Coeur, Arènes de Lutece, Opéra Garnier, just walking around the different areas, etc. Get a good guide book and pick your favorite choices! Personnally, if I had 2 days in Paris, I would go back go the Tour Eiffel, then take a boat tour on the Seine, visit either Musee d'Orsay or Musée Rodin, and just walk around the city the rest of the time (ok I would stop for a glass of wine and people watching...!). Enjoy!🙂