While I understand that Germans probably needed Jewish traders, there are many other traders out there besides Jews, so how could a small group of people boycotting German goods cause a significant effect in Germany?
This site estimates European Jewish population in 1935 to be 9.5 MM, about 1.7% of Total European population. It is unlikely that the Jewish percentage population in North America was much different than that, and worldwide would have been much smaller still.
In regards to a boycott organized by such a small percentage of the population, I see a key prerequisite to it becoming more than a trivial nuisance:
- The organizers of the boycott would have to have been seen as an elite to be emulated, much like modern Hollywood actors.
Given the pandemic anti-Semitism of the time, prevalent even in (more enlightened than Nazi Germany) countries such as the U.K., this criteria was certainly not met.
It seems to me that this was a gesture known, even by its participants at the time, to be ultimately futile, but which was driven by the need to make a stand somewhere.
The Nazis weren't impressed by the Jewish Boycott. It led them to a retaliation Kristallnacht, that accomplished much the same thing, but with a greater impact. Put another way, the boycott may have caused the Nazis to do what they wanted to do anyway.
Kristallnacht had an impact, not so much on the German economy, but on global public opinion. Anglo-Americans, who tended to distrust Germany all the way back to World War I now had a solid reason to do so. Here's a report from the German Ambassador