Sadly the day job will keep me away from Duxford this year.
But have you ever considered leaving your cameras at home and taking (beg it or borrow it: a UHER would do nicely) the best quality tape recorder you could manage, and just record the sounds of the Merlins and the Bristols.
Hours of guaranteed relaxation when you get home listening to the *sounds* rather than looking at the cr*ppy distant photos of a blur on the horizon.
I've always fancied doing it but never been able to get the kit.
Enjoy the weekend
Safe flying
Cusco.