I would be unlikely to drive from Munich to Paris, but you don't say how many days you spent on the trip. I have rented a car in Strasbourg, but that was AFTER visiting Strasbourg, and it was the start of a slow drive to Avignon, about ten days. Another time, we based in Besançon, visiting the Jura and then to visit a cousin in Geneva. But you make it clear that you relish long hours in the car.
I'll mention the common warning given here that you need to learn whether it is safe for you to drive a car right after a night with almost no "normal" sleep. Conversely, some travelers are very disappointed to learn how much effort it takes to get from CDG to the SECOND train station in Paris, to get on the train to Caen. I will admit that we have taken a train from CDG to St. Pierre des Corps (Loire) where I drove 40 minutes to our first hotel after flying from the East Coast USA.
I have driven "back" to Paris from Bayeux. It was a terrible mistake to take the car into the city of Paris, so I'd suggest that you only go that way if you find a place (or are going to CDG anyway) to drop the car on the outskirts. (I'm not a big fan of spending the night at CDG before flying home, but I'm careful to avoid early flight times, if possible. And morning transportation from Paris to CDG isn't that hard. We often splurge on a cab.)
If you are going to "see some spots along the way", I suggest you buy Lonely Planet France, and invest the reading time to find the places that are of interest to the two of you. This is a substantial research job. We chose to focus (I mean, Bayeux-Paris) on public and estate gardens, of which there are a lot in France. I found that most attractions were 20 minutes off the highway, in various directions. It takes a great deal to time to get there, find a parking place in some cases, and get inside the attraction. Then you have to get back to the highway. It isn't a matter of "sparse with good sites", it's that you're not driving from one suburban shopping mall to the next! There's also traffic (especially, local traffic, after you get off the highway) to contend with.
In fact, there are a number of very high-profile, worthwhile locations that are quite easy to daytrip from your Paris hotel, by public transportation. Examples are Versailles, Vernon, and Chateau Chantilly (which includes an important art collection), but there are a lot more. I totally agree that car is very helpful in visiting Normandy. (We even stopped in the local equivalent of Walmart to buy a box fan for our luxury-chateau hotel room, which was mighty hot in July!) I'm not opposed to the car, but rather to the itinerary you've sketched out.
After July in Normandy, you will have spent plenty of time driving around parking lots looking for spaces at the war sites, and waiting for a space to open up, just like Christmas at the Mall of America!