Retirement-Woohoo!! We are two couples planning a 25 day road trip this summer beginning with 3 nights in Amsterdam, Netherlands. Our straw man itinerary is:

-quick stop in Cologne to see the cathedral;
-1 night in Bacharach and 2 in Beilstein;
-Black Forest via Baden-Baden and 1 night in the area;
-4 nights in St Johann, Austria:
-3 nights in Munich;
-travel the Romantic road and 3 nights in Rothenburg;
-3 nights in Leipzig;
- 4 nights in Berlin;
-long drive back to Amsterdam to fly out following day.

This is our first trip to these areas and we may be trying to cover too much in this limited time. Any must see or do recommendations are greatly appreciated. Thanks, in advance.

travel the Romantic road and 3 nights in Rothenburg;>

3 nights would be about two too many for me - a small heavily touristed town that yes is best savored after the day tourists have gotten on their buses or in their cars and gone.

Now if you are going to use Rothenburg as a base maybe but I'd suggest Bamberg as being much much nicer all in all and a better base.

There is nothing romantic about the Romantic Road - a busy road given that monniker by the German Tourist folks after the war to drum up tourists business- the cities it skirts are cute - Dinkelsbuh and Nordlingen especially along with R'burg. Anyway your itinerary looks nice but reconsider Rothenburg for 3 nights and consider say Bamberg.

Leipzig is nice for a large city but it is a great base - nearby are several gems - Naumberg, Weimar, Erfurt and Eisenach - the latter not much but having the famous Wartburg Castle where Martin Luther holed up in hiding once - his tiny cell-like room is still there as are other momentos and Wartburg Castle is a castle of your dreams.

En route to Berlin consider a short look at Lutherstadt-Wittemberg - Luther's city where he nailed demands to the church door (allegedly) - a real nice city with lovely castle and church and of course Luther sites.

Pay attention to speedcameras in Germany.
Last time I was in Germany, I drove 150 kms of which half on secondary roads.
I pay attention because I know the road.
I got THREE tickets.

And only about 60% or so of autobahns do not have speed limits and on them if only going normal speed STAY out of the passing lanes or incur ire of drivers -I had a German truck driver once show me a big knife when I was unbeknownest to me blocking his lane.

If you are determined to have a car, and that's fine and ideal in some ways, why not CONSIDER renting it in Cologne and dropping it even before Berlin; train back to A-dam; IMO you don't need a car In Berlin and even if you wanted to include Potsdam you still don't need a car.

Might save some money avoiding cross the border drop charges but maybe not.

You don't need a car in Munich either but...

Three nights in R-burg is two too many IMO. GO..see the moat, the drawbridges, the walls; roll around inside and the four Christmas stores, etc. and that's about it IMO. Yeah there's that Nightwatchman tour and walking the walls but with so many OTHER things to do, even if you drove down to Fuessen for those Ludwig builds or stopped off at Herrenchiemsee it would be IMO better time spent.