Sorry if I wasn't as clear as I thought, but what I'm hoping to achieve is something similar to what using an ND filter on my DSLR does for me. A little bit more ability to open the shutter (it's bright and hot here in TX right now), and a way to protect a much more expensive lens from scratches and nicks. Turned out to work pretty well even with the ND 16 on my first flight - I'm just thinking a little lighter touch (with an ND 4) would be better for more conditions.
And yes, filters won't protect from theft. But I worry a lot less about that than I do bugs, dirt, birds, and sand