Hi,
True, about the  small number of visitors at the Resistance Museum.   I first got there in 1989 when it opened up and have been back since then  2 or 3 times.  Each time the only visitors I saw were  German, one time a German language guided tour, which I didn't know was offered, ....very good to know. 
I don't recall seeing any foreign visitors, Americans included. 
I would suggest two other sites connected with this history and time period if you want to pursue more in Berlin and its environs.   
One  is the Ploetzensee Memorial (Gedenkstätte Ploetzensee)... pretty grim, poignant, where the conspirators of July were executed. 
The other site deals with the  Russo-German War, the Nazi war of extermination on the Eastern Front.  This is the German-Russian Museum in Berlin-Karlshorst  on Treschow Allee, housed in the Wehrmacht building where the Soviets received the German surrender a day after  their  surrender in Reims, France.   In all the  German signed 4 surrenders in 1945. 
Take S-3  (Direction : Eckner )  to Karlshorst, the bus at the station goes  to the Museum, (Endstation) or you can walk it, I've done both,  ca. a 40 mins walk.   Very enlightening and revealing  in historical portrayal if one is into the Eastern Front  in WW2.