I had, like you, thought for a long time that Nestorius was a heretic. But the current body of evidence strongly suggests that Nestorius did NOT in fact advocate "two persons" in the person of Christ, that rather there was a systematic misunderstanding of technical terms which led to that erroneous conclusion. Please read the following article if you are interested in a detailed examination of the issue:
http://lukebray.wordpress.com/2010/06/02/nestorius-understanding-of-the-person-of-christ-34/
Bottom line, the two-nature/one-person formula of Chalcedon
is the Nestorian formulation. However, the political turmoil led to a condition where his name could not be associated with the the doctrine adopted by the council, but it was his nonetheless. His identification as a heretic appears thus to have been an entirely political gesture, "arbitrated" by invoking the Roman emperor against him, which is completely contrary to Paul's admonition that believers settle such disputes without appeal to human civil authorities. What an ungodly mess it all was.
So yes, Nestorius' concern about the potential for abuse in "Theotokus" was well grounded in an orthodox Christology, and an accurate prediction of trouble to come.
Peace,
SR