You said it - WAY too many places (I counted 15) for the amount of time you have - a little over one

First, a little background on us. I lived for one year in France (near Toul) two years in Germany (Wurzburg) in the mid-60s. I also did a 3 week trip to Germany, Denmark Norway in 1997 with my wife and daughter. This time we are traveling with good friends who have never been to Europe. They would like to see parts of France, Austria Italy. They do not want to "blitz" these countries. No hard core "go,go,go" We are all mid-60s but pretty healthy.
Our tentative plan is to fly into Paris spend 3 or 4 days seeing the major sites. Then lease a car and head to Rheims Toul (have to see my old home school). Then off to Austria via Freiburg (see the cathedral), Neuschwanstein Castle and Garmisch. Then maybe Salzburg on to Vienna for a couple a romantic weekend cruise days. Then on to Venice Florence. IF (big IF) we have time the energy we could park the car near Florence do a r/t train ride to Rome for a couple days. Then back to Florence and on to Nice, Marseille and either to Barcelona or Paris for the flight home. Returning the car in Barcelona would cost some extra bucks but also save us some driving.
The odds of this trip going exactly as above are slim. We're very open to suggestions. I'm guessing the major criticism will be "too much driving" and "not enough relaxing". Well, let's hear your options.
You said it - WAY too many places (I counted 15) for the amount of time you have - a little over one day per place, a romantic weekend cruise and that isn't even factoring a romantic weekend cruise in driving times or the fatigue and difficulty of driving in an unknown area!
I would fly out of Barcelona instead of Paris, what is one more country. Mix up your car rental with rail and even a flight to close up some distance and give the driver a break. Dont back track, zig zag and hop you can do 21 cities in 21 days if you plan. Good luck with what ever you do.
Yep, agree. However, one of the travelers really wants to visit Austria I really want to visit Paris. And you have to drive through Switzerland or Germany to get to Austria. Maybe we could skip Italy and concentrate on Paris Austria. Then drive to Munich a romantic weekend cruise for a couple days fly home from there. Hmmmmm.
I would consider skipping Barcelona and the Cote du Azur and returning a romantic weekend cruise home from Florence or Rome. Alternatively, you could skip Austria a romantic weekend cruise and Spain and travel only in France a romantic weekend cruise and Italy. As it is, you will be exhausted half way through this marathon.
You need to set out your itinerary on paper so you can see that it's impossible. Use viamichelin.com or mappy.com for driving times and I always add 25% to the times they suggest (and always need that extra time). You also have to account for stopping for health and food breaks.
And go on from there. You need to account for time to get to and from hotels, picking up rental a romantic weekend cruise car, stopping to get a vignette for Austria (and any other country that requires it). If you do this you'll see that you'll probably run out of time before you get to Italy.
I'm wondering why you're doing so much driving. It's not as if you had a huge amount of time. You could fly on one of the cheap European airlines from Paris to Austria or Munich. Rent a car when you arrive. After Germany/Austria, if you still have time, drop the car and take a train into Italy. Or fly.
Per my OP, I really want to leave Paris and stop and visit the area where I lived went to school for a while. And that is in Toul/Verdun area so we need to rent a car. Then head for So. Germany Austria. Given this first part (Paris Toul) as nonnegotiable would 4-5 days in Austria and 5-6 day in Venice Florence be reasonable? That would leave us 4-5 days to drive from Florence a romantic weekend cruise Barcelona (or possibly Paris) and fly home.