Do you wash your nike shoe? or not? or how?  

This is really a good question! Although all trainers are not exactly the same, most are made of the same materials. I have been running trails and fell running for the past 3 years. I prefer Saucony. For a long time I believed as you. However I now run them through the washing machine a cool, COOL wash. I stuff them full of newspaper and leave them to dry naturally. This gets all the mud off and leaves them clean. A HOT wash will melt the joins in the rubber, make the foam hard inside. Unstick the inners too. Running with them dirty will erode all the stitching probably faster than washing them. I don't actually care how they look. leaving them gritty inside will also wear out your socks and give you blisters too. On balance washing is probably best. The harder you work them the quicker they wear and its not just about sole wear. Got to face it they may not last 6 months.