so as to maximise your time and money, i second the Orangerie/ invalides/Rodin idea.

you could also do the musee du moyen ages http://www.musee-moyenage.fr/ if you weren't completely exhausted.

St. Denis is way out of your way and you will spend a lot of time getting there and back, so if you want to go there, i suggest doing it on a day when your museum pass has run out.

Thanks to all for your terrific suggestions. We opted for the Rodin - a great choice- then went over to Montmartre for a 5:00 walking tour given by Discover Walks - It's free but they make their money through tips. (we gave $40 for the two of us) Bruno was our guide and he was excellent. We then had dinner at what turned out to be the oldest cafe in Montmarte, Le Bon Bock.

We will definitely try some of your suggestions in the next few days

PS We almost learned the hard way that the Metro doesn't run all night long when we almost got trapped inside!

haha glad you didn't get trapped. I had to walk back to my hotel after being trapped at Charles de Gaulle station around midnight. fortunately it's a very walkable city. have fun