I started to do a similar work whend i was on the lower levels, but just give up, all things seems a bit random, it is impossible to get to a fórmula you can apply.
As you i have concludente that fast trainers lose more market value at the beggining of New season that slow trainers. Players above 32 years old do not lose any value, they keep the same.
Whend people say about relation between MV and wage that work for nordgens.