The speed is more than just a little important in the OF, where he is easily one of the best LFs in the game. Crawford is a dangerous threat on both sides of the ball.
My only hold ups for him are:
1) Not sure where he fits in this lineup (3rd?), especially because of the benefits of the L, R, L, R preference.
2) He will cost a lot
3) He seems vulnerable against good LH pitching. (.256/.696 v. LHP; .332/.930 v. RHP). We would prefer him to hit well against RHPs (which he does) but in the AL East there are some really good lefties who the Sox will need to beat.
I don't much care if he's a "superstar", that role may be limited to 5-10 players at any one time and he's not the most famous/impressive player. He's still very, very good.
I agree with others who see him signing in Anaheim. I think the Sox should be able to outbid just about anyone but the Yankees if they really want someone. I would be surprised to see them pay Crawford more than $17m a year, but I think it'll take at least $18.5 to get him.