I'm slowly but surely coming to the reality that a player must have a very high % of steals vs CS to help the team in this game.  My next question ... if you put your Base Running Aggressiveness to Agg. or V. Agg. And only set high % " stealers " at  3-5 will your high speed rated players take extra bases or score from 1st on certain hits if set at a 0 ? 

base running and base stealing are two separate events. The setting for one does not affect the other.

I don't think base stealing stats figure into success rates in taking extra bases in relation to the baserunning aggressiveness setting.  And if you have a guy set to 0 on the individual base stealing, I don't think that stops him from trying to take an extra base if the team aggressiveness setting is 4 or 5.  The speed rating will have the biggest impact on the success rate of safely taking the extra base.  The setting itself will only determine how often guys go for the extra base.