I too have had numbing toe issues after a day of riding. My numbness usually comes after about 4 hours of riding. Its a bitch since it usually always happens and even if my legs still have some strength, I have to end my session because my feet kill. Over the holiday's I rode for 6 days straight and the tips of my big toes were numb for days afterward.
It worries me because it cuts my session short and also, like many of you, I don't want to have long term nerve damage.
I've tried a bunch of things over the 10 years I've been riding, arch support (I have extremely high arches in my feet) helped and keeping my inners loose helps as well.
I've come to realize though that even with all the tips and tricks I try to do to avoid the numbness, it still happens and I think the reason is the constant (or almost constant) pressure on my toes when riding. I like to ride hard which means digging a deep edge, which means putting a lot of pressure on my toes. This constant pressure, after many hours, leads to numb toes. I just don't think their is hope.
If anyone thinks differently, let me know.