so far,it hasn't made a difference.
The main problem is that the super sub is normally a player who isn't good enough to get into the 11 in the first place so he's not likely to make a significant contribution anyway.
lets take 2 scenarios;batting first and second.
scenario 1-batting first
England play Solanki as super-sub,they're in a bad position so they sacrifice a bowler in the hope of getting extra runs,Solanki makes 60* to get England up to 200. Problem is,200 still isn't a very good score especialy when they've sacrificed a bowler to get it.Australia end up winning comfortably,to make any difference on the match,Solanki would have needed to make a very very quick 100,which is very unlikely.
scenario 2-batting 2nd
Australia make a good score,around 270ish,England sub Harmison for Solanki to bat 6/7.Now 2 things could happen here,England get stuck in a rut and Solanki needs to make a quick 70 odd or England cruise to victory.Either way,the super sub is questionable.If England cruise to victory then he wasn't needed,if he plays a significant part in winning,its unfair on Australia because England had
effectively played with 12 men.
TBH i'm not sure what the ICC were thinking when they made it up,batting 2nd you get an un-fair advantage,batting first if you sub a bowler your usualy going to end up with a below par scorw anyway,and without a 4th/5th bowler tod efedn it its even harder.
The power plays are an idea from 1996,not 2005.If every team opened with Afridi and Jayasuria,them maybe,but the fact is that no one does anymore.In every game i've seen,the captain has nealy allways played the powerplays in the first 20,even if the opposition has got a good start.