There are direct trains from Würzburg to FRA airport station that typically take 1.5 hours. You might spend 2 nights there, see the Residenz in town, and perhaps take an outing to the most spectacular city in the area, Bamberg (just under 1 hour by RE train.)

Thanks, that sounds appealing.

I forgot to mention that we'll have a car.

Würzburg can well keep you busy for a while, there is a lot more than just the Residenz. I highly recommend the climb up to the little pilgrimage chapel named Käppele, and of course also to Marienberg castle, take the trail through the vineyards even though it is longer, the views are fabulous.

Be warned, you might end up in hospital in the evening...

Old joke in our family The two historical hospitals, Bürgerspital and Juliusspital, own the best wineries in town and the restaurants/wine bars of both are an excellent choice to spend the evening. Hope you like dry whites?

You may want to have a look at my Würzburg travel page over on Virtualtourist: http://members.virtualtourist.com/m/f86bd/14f6/

If that sounds good, drop the car in Würzburg - then on the morning of your flight, you don't have to mess with the car and the shuttle to the terminal; the train gets you right to the airport. Before that you might use the car for your Bamberg outing and then drop it in W'burg, or you might drop it when you first reach W'burg and use the Bavaria Ticket (26€ for two round trip) to visit Bamberg.

http://www.munich-touristinfo.de/Bavaria-Ticket.htm

W'burg - FRA by train: regular fare is 76€ one way (ouch) but you can usually get advance-sale tickets for two for 29€ total or thereabouts at the DB website:

http://reiseauskunft.bahn.de/bin/query.exe/en

It is a very good idea to go by train rather than by car from Wü to Fra.
1. The train connection is excellent.
2. The airport train station is really next to the departure gates of FRA.
3. The autobahn A3 from Wü to Fra is highly congested, particularly during rush hour. No fun drive

In Rothenburg you will undoubtedly see the beautiful Holy Blood altarpiece by sculptor Tilman Riemenschneider

The Mainfränkisches Museum in Würzburg has the world's largest collection of works by Riemenschneider who was a mayor of the city.

Since you do have a car, my suggestion is to do something a little different than you propose -- visit a number of the lovely SMALL towns between Rothenburg and Frankfurt, arriving in Frankfurt the night before your flight so you won't be stressed the day of your flight.

There are some darling little towns that you could spend an hour or two walking through -- Miltenberg, Wertheim, Iphofen, Dettelbach just to name a few. We found these towns to be real gems and they are all in close proximity to the much larger Wurzburg.

Miltenberg: http://preview.tinyurl.com/ap5kugt

Wertheim: http://preview.tinyurl.com/b3pce24

Iphofen: http://preview.tinyurl.com/am7qu62

Dettelbach: http://preview.tinyurl.com/aff7fw9

Some links that might be useful:
http://www.frankentourismus.com
http://www.fraenkisches-weinland.de
http://www.wuerzburgerland.de/en/wuerzburgerland.aspx
http://www.wuerzburg.de/en/visitors/index.html
Indeed, the small franconian towns are really beautiful.

From Rothenburg back to Würzburg, you could avoid the Autobahn and go through
Weikersheim
http://www.weikersheim.de/english_version/index.html
Aub
http://www.stadt-aub.de
Ochsenfurt
Creglingen
http://www.creglingen.de/3247.php
http://en.ochsenfurt.de
Tauberrettersheim
http://www.tauberrettersheim.de
http://www.roettingen.de/index.php?id=107
Sommerhausen
http://sommerhausen.de/startseite-english.html
Check the map here:
http://goo.gl/maps/WZsFs