Adding a second week to a tour of Luther-land -- Best options?

Trains will take you nearly everywhere, so you don't need a car unless you identify some destinations that are not served by rail. You would not want a car in Berlin or Prague. I would focus on the closer options, including more time in Berlin which really has a lot to see, also Dresden and Buchenwald Concentration Camp memorial, reached by bus#6 from Weimar train station.

If you have time for more, then Prague is an exciting detour.

Right by Wittenberg, check out the huge English garden landscape of Wörlitzer Park. It might, however, be a little less impressive in October.

If you like zoos, don't miss Zoo Leipzig. It's one of the best in Europe.

Hi,

Going from Berlin Hbf to Lutherstadt Wittenberg is a direct connection taking the ICE train. From the station you can walk to the Altstadt, ca 20 mins or so.

Another way of going to the Buchenwald memorial camp site from Weimar is to take the bus from the Goetheplatz. Signs there indicate which bus.

"...exploring other Saxon towns." I heartily recommend Meißen. If you're going by public transportation, take the S-Bahn from Dresden Hbf. The town is considered as "die Wiege Sachsens" (the cradle of Saxony), survived the war with hardly any war damage.

Some ideas in this area (Eastern Germany):

Harz mountains
The Harz mountains are ~90min to the northwest of "Luther land". They offer some of the best preserved towns of Germany, among them Goslar and Quedlinburg (read the reviews here), two World Heritage Sites, but Wernigerode, Stolberg, Wolfenbüttel, Celle or Duderstadt are equally nice. They can easily compete with the towns of the Romantic Road, which aren't that unique. There are also some fantastic churches in Hildesheim and Halberstadt, the largest steam train network of Germany, and the mountains itself of course. The highest peak of the mountains and of Northern Germany, the Brocken, can be reached by a steam train.
Here is a gallery with 130.000 pics of the region. Have a look at the places I mentioned:
www.raymond-faure.com

Saxony
Saxony offers a perfect mix of everything. Small towns (Meissen, Freiberg, Bautzen, Görlitz, Pirna, Torgau), world-class museums (the collections of Dresden), big cities (Dresden and Leipzig, the "new Berlin"), vineyards and wineries (Radebeul), picturesque mountains (Saxon Switzerland, Zittau mountains), castles and fortresses (Kriebstein, Königstein, Oybin, Pillnitz etc.), unique traditions (the Ore mountains are Germanys Christmas country... all the year round) and villages (around Zittau), and parks (Bad Muskau).

Baltic coast
This region, 3h to the north of Berlin, is the second-most popular tourist destination of Germany after Bavaria. Not only because of the long, sandy beaches but also because of the posh resorts, beautiful nature (especially on Rügen island and the Darss peninsula) and historic Hanseatic towns, which are World Heritage Sites. This is the perfect mix if you want to relax and see some historic sights.

Near Erfurt is Weimar (Herzogin Anna Amalia Bibliothek, Goethe and Liszt museum, etc..) itself of interest and if you like J.S. Bach you can visit in Eisenach his birthplace/museum. For modern architecture/design is Bauhaus in Dessau not to miss.

I second the choice of Weimar. Goethe and Schiller am Theaterplatz in Weimar can be seen also in SF.

Spend more time in Berlin if you can. I don't know if Augsberg fits into your Luther-land plans.