Well there haven't been too many suggestions, so let's look at some more.
1. Were the Mapsource based routes I pinged up any good? I appreciate that they started and ended in Calais but it would be easy to just ride nearly straight down from Caen to pick them up.
2. Caen brings you out into the very popular D-day invasion beaches area. As the beaches cover a length of about 80 miles, east to west, and each has its own museum, things to see or whatever, you could clock up four days and still not see the lot.
Add in going to see the Bayeux tapestry and your four days will be over.
3. Don't fancy guns, tanks, gravestones and concrete blockhouses? 11th century needlework not appeal? OK, maybe head off deeper into Normandy and Brittany, perhaps? The standing stones at Carnac, Mont St Michel, maybe the U-boat pens?
4. Still no good? How about the pretty decent racing museum at Le Mans? It's right near the main entrance. You can also ride around long lengths of the 24 hour track, pretending you are in an Audi at over 200 miles an hour.
On south from Le Mans and you are into open France. Rivers, bonkers chateaux, woods, great roads. You name it, it's there and then some more.
5. Have a look at the 80 Virees Michelin Moto stickies. It's to answer questions like this that Michelin created them. Stitch a few together and you'll be fine.
Not got a GPS or can't open Mapsource or Basecamp (one day I will get around to converting them to .gpx) no problem.... Get yourself a 1:200000 scale map and plot your owne routes out. Not sure how far to go? If you are riding reasonable D roads, 250 miles is a decent day's schlep. Stop every five minutes to gawp and press wild flowers and the day will vanish. Add in some motorway ( there is nothing wrong and no shame in riding on them, not least we'll never know) and 350 miles - 100 of motorway plus 250 of D roads - becomes a not unreasonable day out.
6. You found your way to Luxembourg from Holland. Be confident and you'll find plenty to amuse starting from Caen. Really, a map is all you'll need and a bit of Google work.
Google:
Things to do in Normady
Things to do in Brittany
Motorbiking in Normandy
Motorbiking in Brittany
I just did and got some pretty good ideas. Just click on the Google links and see what comes up. Surf away, you can't break it. Find something interesting, save the URL and come back to it later. Have a look at some of the organised tours; not because you necessarily want to join one but because they often give a clue as to where it is they'll be going. Join the clues up and Bingo! You have made your own tour. Last but not least, have a look on UKGSer. Hit the advanced search function, just typing in a key word like 'Normandy'. 100's of threads will pop up, just click on few that look like they might not have started in the 1200 Technical section.
Let us know what you decide on please. Yours is a common enough question... Who knows, what you do might be just what another bod will want to repeat in October 2014 or May 2022.
Have fun.