One of the issues Americans have in Europe and especially in France is when we enter any establishment (food, shopping, hotel, etc.) our first instinct is to say, 'I want ...' or 'I am looking for...' or 'Can you ...' etc. And a European's first words are 'Good morning', 'Good afternoon', or 'Good evening' in whatever local language. It is a simple acknowledgement of the proprietor as a fellow human and without it we Americans appear rude and pushy. I found a surprising change in attitude when I learned that simple lesson from a friend.
I loved my short visit to Bayeux to see the tapestry but was headed for Mont Saint Michel (fabulous) and didn't do the WWII sites on the trip. Would love to do both those and the WWI sites as well. Two great generations not just one. (I visited Oxford with my father who was there in 1936-38 and we visited the wall honoring theWW2 war dead at his college as he pointed out all his friends names - from his 2 years at Oxford he only knew two Europeans who survived the war. Europe truly lost 2 full generations of men in a 30 year span)
Love Paris and London - I would recommend looking into the various tourist passes you can purchase either before you arrive or when you arrive. They give free admission to many museums and sites, and usually have a separate entrance or allow you to skip the line, and some give you free bus/subway travel as well. They have various time limits from a day to a week and get a time stamp the first time you use them.
One of my favorite small museums in Paris is the Musée Rodin located in his former studio and the grounds. There are other small museums that are fun as well - a Picasso one, a Delacroix one, etc. I recommend searching a map of the area around wherever you are staying to see if there are any little gems hidden in easy walking distance for when you have an hour free. It may not be something breathtaking, but it maybe something you treasure more than the flashy tourist places everyone goes. (Same can be true in both England and Ireland - so much history and culture especially to us who have only a few centuries of history around us.