I know this is an old post, but I just noticed it now, and I'm assuming they're having the event again this year (2009).
I rode to this event from Baltimore last year (and I'm an AMCA member), and for those of you who are expecting this vast contingent of cafe racers there, forget it. It's heavy Harley and Indian, which is perfectly fine (this is an AMCA event, after all), but I was definitely in the minority there with my '66 Honda CB77. The VJMC had a nice sized booth, and there were displays of vintage trucks and steam engines, which was really interesting to see. It is a fairly new event, and it's much smaller than Mid-Ohio. Overall it's worthwhile attending, though I don't know that I'd ride my CB450 cafe racer from Toronto for it. The area is definitely beautiful, and there are several good B&B's in the Rhinebeck area. Plus, you're close to Hyde Park (home of the Culinary Institute of America), so you know there's going to be lots of good restaurants in the area. If you do decide to go, book your hotel now!