Janet: thanks for doing that! Seventeen does not seem an impossible number to write to - I have considered it before, but thought there would be more. Funny that there are 17 Zochers too!
I do know that my great grandfather was born in Dresden. I have his birth and baptism records. Similarly, I have quite good records of his antecedents - who originated from Pirna just upstream on the Elbe and were originally "brandywineburners" (meaning distillers) Alfred had a degree in chemistry from Gottingen University and he was a real go-getter in that he pioneered sugar refining in Germany, later on Long Island and then in Montreal, where he became very rich. There is an (inaccurate in part) Wikipedia entry for him. To answer your question, no, there are no family left in Canada (where my mother was born) but some Baumgarten descendents in the States, who I am in touch with. They are descended from Alfred's second daughter. I am descended from his first.
The big puzzle is what family there might have been left in and around Dresden - more likely relatives of Alfred's mother, i.e. Zochers. I may well write to the Baumgartens and Zochers in Dresden, now that I see the task is not impossibly big.
Thanks once again. You have been very kind.