Paul, I thought this idea was great until I spent time making some to use on the JMT last summer.
They were so bad, that we just ended up burning them the first chance we got. They were terrible. Dirt, twigs, and pebbles would work their way in after a step or two and our feet (or socks) were filthy after a few minutes. We were much better off in camp with our shoes on with the laces untied.
We also used DirtyGirl gaiters that kept the insides of the shoes relatively clean, so wearing clean socks in the shoes in camp worked out well.
Now, using five finger shoes makes this a bit of a dilemma. And, yes, the Tyvek booties may work, over some thick socks, especially since your feet should be well accustomed to debris you may step on.