Hi there lyndijon and hello again Poecile
I've had exactly this same problem. My Nestboxes are more like 20ft apart but I too have one with and one without a camera. If you read my post
http://blog.shirlsgardenwatch.co.uk/2008/03/arch-nest-box.html you will see what happened when I blocked off my non camera box.
We have one pair visiting both Nestbxes and you can read the latest here
http://blog.shirlsgardenwatch.co.uk/2008/04/who-makes-decisions.html. I really don't know which way it will finally go. The female likes the camera box but the male seems to be bossing her to the other.
Ah... they will probably use the one without the camera. This is only our second year with the camera box and last year after a week all our eight chicks died. It would have been nice to see a successful brood fledge from our camera box :-D
Fingers crossed - good luck with yours :-D