When I did a yoga class a year or so ago, I discovered that I was completely unable to stretch my toes. I also couldn't cradle my feet with my fingers between my toes as it made me queasy. 
I started walking to improve my fitness and quickly developed plantar fasciitis. It has returned again, and I was wondering if it could be linked to my unbendy toes? I saw something called 'Yoga Toes' which are plastic/silicone toe separators and wondered if they would help?
Does anyone have experience of these or something similar, or could recommend some yoga exercises to help flexibility in my feet?