I'm around the Toronto area fwiw. I'd say on a typical day I see about 1 out of every 75 male riders riding a mixte. Usually an older gent, though I've seen maybe 1 or 2 younger men riding a mixte over the past 2 months.
I've been trying to calculate how many riders you see each day, but I got confused ...
Speaking of older gents on mixtes and collectibility: take a good look at this old Batavus mixte:
Looks like a POS, right? It is. But the owner, whom I saw riding in on it on that particular day (and who was the only reason I photographed the poor thing) was the man on the left in this picture:
In this photograph he is congratulating Fausto Coppi on his 1952 Tour de France win. They know each other, as both were on the world championship podium in 1949. Fausto came in third with the pros, and Henk Faanhof was the amateur champion.
Now, is that Batavus mixte, owned by a former world champion, collectible or not?