Funny you should ask!
I spent a week in a FeWo in Gengenbach in September a few years ago...
Loved the town, WAAAYY less touristy that RodT..often called "the Rothenburg for Germans". Half-timbered houses, cobblestoned main square, tower museum of Fastnacht costumes of the past centuries, climb up to chapel above tower/through the vineyards for a wonderful view over town, area produces a wonderful Rose wine and ...if you time it just right...in mid to late September-October---Neuer Suesser/Federweisser shows up on the menu!
I used Gengenbach as a base to visit nearby Gutach with its fab 'outdoor museum', and to visit Strassbourg and Colmar in Alsace---wonderful towns as well--heartily recommended.

Shhh. Too much press about places like G'bach, mokka4, and they get trampled like Rothenburg has.

More differences between Rothenburg and Gengenbach:

In G'bach, German is widely spoken.

There is a Nightwatchman in G'bach, but he also speaks German. Meet him on Wed or Sat at 21:00 at the town hall.

http://www.stadt-gengenbach.de/de/tourismus/tradition/nachtwaechter/

Gengenbachers don't know who Käthe Wohlfahrt is or what one does with Schneeballen.

Enough of the R od T bashing already.

Gengenbach is very small compared to R od T. I loved it but it has less to keep you interested than R od T for a visit of more than a day.

Gengenbach, is not "wonderfully" situated - it is not in the Black Forest but snuggled right up against the western edge. It does provide access by virtue of that, but I find Franconia's rolling hills around R od T to be more interesting, geographically, than the Black Forest.

The kicker may be that, in September, you would have access to the Alsatian wine route towns and their festivals from Gengenbach.

www.vinsalsace.com

Lots of wonderful towns there. In fact I would probably base there as there is more to see in a concentrated area, Strasbourg to Colmar, primarily - and visit Gengenbach on a day trip.

Thanks mokka4, Russ, and Aramis. Maybe it would be better to do Gengenbach as a day trip from Strasbourg and save the 2 nights I had planned for Gengenbach to visit Salzburg or the Cannstatter Volksfest near Stuttgart... Any thoughts? Thanks for your inputs...

I have always wanted to do the Volksfest but have not made it yet.

I would take 2 days in Salzburg anytime - and usually do.

If you truly "travelforbeer" you should consider spending a day at the Cannstatter Volksfest. It's closer to your other destinations than Salzburg.
Gengenbach is worth an overnight and I prefer it to Rothenburg.

Wonderfrau- Thanks for your suggestion. I just checked and the Volksfest does not start until 28 Sep this year and I have an early morning flight out of Frankfurt the 30th. And my FF hotel in Stuttgart isn't accepting reservations starting on the 27th. Maybe next year...