We've been 3 times. The first time, we booked an apartment through RentParis.com. Had a nice place for the 4 of us near the Pompiedeu (modern art museum) for about 100Euro/night. We did have problems with the contact numbers, so make sure they are working correctly before you fly there. We ended up having to pay $300/night for 3 nights (there goes the Disney money) for a Holiday Inn before we finally got a hold of the company, which was very nice, but wasn't planned. Second time, my husband and I stayed with specialapartments.com in a one bedroom in St. Germaine for around 75E/night. Third time we took the kids to Disney and the Normandy beaches and stayed at the Explorer's Hotel near Disney. I wouldn't recommend it.
If your intention is to see Paris, stay in Paris. The train ride out to Disney isn't too bad, but if you get there late, you'll be taking a long walk to your hotel from the train station. I'm talking, we arrived one night at 12:30 and there were NO buses, taxis, shuttles.
As far as things to see: Musee d'Orsay (Impressionist art--fabulous), The Louvre, Versailles (short train trip), Notre Dame, another cathedral almost across the street from ND that I can never remember the name of but has AMAZING stained glass windows, Arc de Triumph (at sunset is remarkably stunning), and the city itself. One of our trips we came back with a picture of the storefront window of the exterminator's shop. Taxidermied rats from the 1880s (EWWWW...but the kids loved it). You never know what you'll see just wandering around.