Have just had another look in Marianne Palmer Bonz’s The Past as Legacy: Luke-Acts and Ancient Epic and rediscovered the obvious original inspiration for my view of the we-passages in Acts. She writes, after discussing the other suggestions up to the Robbins and MacDonald views:
The “we” passages do not represent historical, eyewitness accounts. But while they are, therefore, rhetorical, they were not created to add verisimilitude to Luke’s historical narrative. Nor was Luke merely attempting to follow a literary convention for certain types of adventurous voyages. Rather, the “we” references serve as rhetorical shorthand for the Pauline Christians — those who are vicariously privy to Paul’s example and who, as heirs to his legacy, have been called by him to continue his unfinished mission. They are Luke’s intended audience, whose participation in the ongoing drama of God’s salvation plan is signaled by the words of the Luke prologue: “concerning the events that have been fulfilled among us“. . .’ (p.173)
What I am attempting to do is to elaborate on this, though not necessarily in the way that Bonz herself might go. I am seeing the “we” less in terms of Pauline Christians per se than in the targets of the revised founding myth.