Orson & Jazz, Tony: I would like to read such a symposium, too, but aside from a few alive who actually worked on Welles' projects like Christopher Lee, there are not many of those personalities still alive. The book would have to be made up transcripts of film biography docs (like Huston's memory of why and how Welles gave his Father Mapple performance in MOBY DICK), or collected and uncollected bits from interviews in already published books and magazines.
It may not be much of a movie, but the best fairly recent collection of such memories is Graver's WORKING WITH ORSON WELLES (1993). Besides the Boswellian Peter Bogdanovich, there are lots of anecdotes from the likes of Stacy Keach, Peter Jason, Susan Strasberg, and director Curtis Harrington. Not exactly on the same level of Joseph Cotton or Agnes Moorehead, perhaps, but very interesting, and sometimes amusing.