The problem is there are a lot of flaws that can't be fixed.
For example, speed. You either have it or you don't. Acceleration, on the other hand, can be taught and improved.
The other problem is that a lot of the guys have quite frankly reached their zenith or started to decline. There is only so much you can do with training. When you get to a certain age and you been playing ball for a certain period of time, there is very little you can do to correct most of the technical weaknesses you display.
Take for example, Carlos Edwards. He is almost 30 and men saying he needs to improve his crossing. The fact of the matter is his crossing is what it is. If after two seasons at Sunderland, playing in the EPL he hasn't been able to improve, it very unlikely to happen, injury or no injury. His crossing was just as bad before.
Where Carlos excels is in delivering little chipped balls into the box, when he has the confidence to dribble a defender to get close enough to chip it in - like for Latas goal against the USA. So he needs to work on taking on his man more. As far as whipping balls in, right now, we should be glad when it just manage to stay on the field, as far as I concern.