That kind of drop is too much for me to consider it to be "worth it". I've had guys drop 4-15 points and left the redshirt on, but even at 15-20 points I even consider it to be a breakeven proposal at best.
The whole point of the redshirt is to give him time to develop, but unless I'm really off base on this, I think a guy at 59 WE for his whole career will with four seasons almost certain develop faster and better than a guy at 20 WE his whole career but with five seasons to develop instead of four.