I feel like this decision has to be taken as him not liking the current staff and wanting to move on. There just doesn't seem to be any financial incentive to him declaring early. I would love to know more about the discussions he had with his family and the draft report to get a better understanding.
When a player declares early, they are basically mitigating their financial risk of getting injured and hurting their earning potential as a professional player; however, once you get outside of the first two rounds, the contact values (and bonuses) drop substantially. For that reason, I think it's always in the players best interest to try for that breakout year that is going to vault him into the first two rounds. Think of his senior year as more of a showcase to NFL teams. As it stands now, he is more likely to be drafted in the lower rounds or not drafted at all and an injury plagued or low production year isn't going to affect him nearly as much as that is already his draft profile. In other words, another season could only help him.
I think Collins is also making a mistake, but Valentine's decision is an even bigger head scratcher.