I proposed 18 months ago on the Eiffel Tower, then returned 6 months ago for the honeymoon. Each trip we also drove for a week in a different part of France. Can't go wrong with Paris in my experience.

Few things, first you will need 100K miles for coach and 200K miles for Buisness. I think the first response was pretty good because you need to get the tickets ASAP. Remember you can always cancel them if you get better later. If you can get the 100K AA miles quickly and book something up, then maybe go for the Chase Hyatt for each of you to get the 2 free nights each at the Vendrome.

I've been to Paris many times and prefer September over all other months myself. other Paris tips: Museum pass, Metro pass, Metro iPhone app. Don't get hung up on the Louvre, make sure to visit the Musee D'Orsay, and take the nighttime boat tour of the Seine.