The Almanzo is definitely an eroica event, though not limited to C&V. enough broke-ass kids do it, though, that half-ish of the field is riding vintage steel, just 'cause that's what they have.
The West Side Dirty Benjamin is another gravel grinder in Minnesota, less hilly but a lot faster than the Almanzo. My buddy Kesh who races for Omnium Bike Shop's CX team rode it last year on his Centurion and placed IIRC 5th or 6th, and he's one of these guys with melon-crushing thighs who never smoked a day in his life. Quite a fast field, and they say it can be a lot of fun if you're in condition for it.
*I* say that any event you're in can be a C&V event, as long as you're on a C&V bike. I can definitely say that my Raleigh Professional gets a lot of compliments in the alleycats.