The "drift" here has been much more interesting than the originally-intended topic. Thanks, Art, Don, LH, Bonnie et. al.

A footnote to the discussion of how much or how little "Mitch & Mickey" might have been modeled upon Ian & Sylvia:

Check out the "DVD extras" packaged with the film "Festival Express" and look for the interview segments featuring the latter-day Sylvia Fricker commenting on her long-ago experience. It's difficult to believe that Catherine O'Hara didn't watch that same footage and digest it thoroughly as she worked up her "Micky" character for AMW. Lots of the same mannerisms, etc.

Of course, the real-life Ian Tyson probably has much less to do with Eugene Levy's spectacularly neurotic "Mitch," so the parallel between the real-life performing couple and the fictional one is far from complete. But there is certainly enough commonality to argue that M&M are, to some extent, "based on" I&S.