I live between US, UK (and soon the Phillipines) and while my schedule is my own, I usually have meetings, visits, appointments et al booked up for several months in advance. If I was already (scheduled to be) in the US during the seminar, I would most definitely come -- partner in tow! If I had more than 6 months notice (i.e. if it is next year

), I would do my best to shuffle my travel plans to attend. Anything else, I'd still really like to be there, but logistics might make it difficult. Even with two of us to pay for, I think $300 is a good price point.
I read both of your blogs regularly, and wouldn't want to have to pick between simultaneous talks by the two of you. I don't mind how big the attendance is, and I appreciate that a larger attendence makes for better economies of scale. Some interactivity can be fun, but it's also easy for it to feel forced and trite, especially with large groups when huge amounts of time can be lost to trivial exercises.
As a long time lurker I too would like to have new material to absorb, and a light enough schedule that there is still time to socialise and maybe see a show... perhaps a semi-formal meet and greet to network with other attendees would be a neat way to get to know the introverts? Although I'm sure you can invent a novel ice-breaking activity to add interest.
Did I miss anything?