I have a collection of shoes with lightly worn outsoles whose midsoles are compressed at the ball of my foot. This is a problem since when this happens I get joint pain on the second and third toes of my right foot. This compression typically occurs between 200-300 miles- earlier in shoes with a softer EVA foam- and considering the cost of running shoes this is no good!
I decided to try fixing it by applying some silicone caulk to fill in the dent in the midsole. The idea is to use caulk to repair the midsole from the inside - as opposed to the old "Shoe-Goo" repairs we used to try to do on our outsoles.
The procedure is to apply a puddle of caulk in the depression, lay an old credit card over it, press down to flatten the silicone, then slide the card off from the side, lifting it out and using it like a putty knife to restore a flat surface in the shoe. Cure 1 day, reinstall the insole and try it.
Here are the first two reclaimed pairs: