I don't factor in WE when to redshirt a guy. I just do it based on who I want to boost IQ. Usually try to redshirt all my PGs so that they have at least an A rating in both OFF and DEF by the time they're starters.
Also, it could be argued that you're better off redshirting low WE guys since they're more likely to need the full 5 seasons to max out their ratings than a player with a 80+ WE.