As far as I'm aware the players' stats just get updated and so do their values, be it good or bad.
I had Obinna in the beginning when he still had 90+ stats for his agility, top speed, dribbling speed etc, then all of a sudden he was downgraded in all of his speed stats (all yellow instead of orange). I didn't get any extra money or anything.
So if I were you I'd watch out with players like Kaka, Ronaldinho etc who haven't exactly had a good season. If they get downgraded then teams will potentially be robbed of several millions. In theory, it also works the other way. Someone like Cahill should surely get his stats boosted so that his overall is 80-85...