I've previously mentioned on a similar thread that you can get some heavy duty thread and a needle from somewhere like a saddlers or shoe repair shop. I repair my stitching as soon as it starts to split and my shoes seem to last a lot longer as a result. As Stumpy says above washing them (even if its just in the beck with a nail brush) seems to help but it also means you notice the damage or wear and tear at an early stage and can do something about it.