longevity of iPad Smart Cover
The smart covers, generally do leave the vertical stripes. This happens when the fold areas of the cover do not touch the screen when it is closed. If you remove the smart cover fold it up and hold it horizontaly while wiping down the screen you will remove these stripes. 

I have found that after owning 2 covers, both ployuretherene, that the microfiber lininng does start to fade away, but this like most things will be determined by the amount of use, and whether you take care of the cover.

Try not to let the microfiber part touch any dirty surfaces when it is off, or you are using it as a stand.

To clean the microfiber lining you are better to use another microfiber cloth.

They have changed since first release. My first one was a lighter green on the outside and grey on the inside, the covers now all have matching inside colours and slightly more contrast in the clolour of the outside