I'd have to take out a second mortgage on my home if I bought shoes every 500 miles. Or get a second job. Maybe I'm just not fast enough to tell the difference, but I have a pair of shoes with over 2500 miles on them that I keep going back to just cause they are more comfortable and I don't want to wear out my new ones
. I do get new insoles for them every so often though. I do run quite a bit on the treadmill, and think the treadmill is much easier on shoes.