I went up to Duxford in the last week of October and can say it was well worth visiting even without the air displays.
Worst part of the day was the rail epic from Kings Cross to Cambridge. At £16 for a day return ticket that could take over two hours each way (did for me), it makes the bus from Victoria Stn at £9 return and 1:30 each way look good. Online bus tickets can be purchased at
www.gobycoach.com