These have all been great posts, advice and suggestions.
We are on award travel (Saver)
I think with that long of a layover, getting out of the airport for little while would be nice.
A few follow on questions and comments:
1) Which lounges actually have a shower? I am not so worried about getting a bed or a nap in FRA as much as having a chance to clean up and freshen up.
2) The idea of a day room is not a bad idea. I've used that before.
3) I will try to get into Lufthansa F if it pops up but since we are on Saver I am betting the opportunity for that will be super low.
4) If we go into the city (or anywhere out of the airport) what are our bag storage options?