IMO a redshirt year is going to be worth about 40 to 60 points on average in total rating, but that depends a great deal on potential and work ethic. I'm a firm believer in redshirting, but I tend to redshirt based more on what I need at the moment vs. what i think I'll need when the player is a senior.
So in your case I wouldn't look back. You got the guy to take the shirt. Be happy. Last season I had a guy on my D2 team who refused 2 shirts and lost most of his WE when I tried to leave it on, so I gave up. I wish I would have kept it on him, now.
I had a somewhat similar choice in my George Fox team this season. I have one SF with a lot of high potential areas but low rating (437) and a PF with higher ATH/DEF but cruddy offense. I usually would 'shirt the SF so he could reach full potential by the time he's a senior, but this season I think the SF is going to play so I redshirted the PF. Once my upperclass bigs graduate, that PF is going to be a central part of my rotation and this way he has an extra year to work on his jump shot.