My point of view is most teams should have a Corner Specialist and a Free-Kick specialist. These guys makes a lot of difference. Especially Corner specialist that helped out to win the League with really high number of assists.

Last season I had 2 Corner Specialists and only 1 of them really made the difference. But the funny thing is, I play both of the frequently almost in every match. But the one that is really not so good in corners level up with a star while the other good specialist stays the same. Both are on equal quality and the one who is not that good leveled up first and scored a lot of goals.

As for free kick specialists, I have had one in every season except for season 4. I do feel there is a lot of difference with higher percentage of the goal going in is better. On season 2 and season 3 I kept 1 player for 2 seasons for his free kick ability. Let's just say out of 10 tries, he will score at least 8 of them and assisted a lot more that season.

Other free kick specialists such as Shadow striker, aerial defender, dribbler, 1 on 1 stopper and penalty specialists are mostly useless in the game. I have had all of those and they make not much difference. 1-on-1 stopper works and aerial defender sometimes works. The word is sometimes.

As for training for SA, so far in my 6 season experience, I don't recommend it. Because they would split the experience that they learn during the game. You are better off buying those who already have the ability. Usually look for those who are a bit more costly, the price makes a difference in my point of view.

I am only 6 season in, just sharing what I learn about the game I am addicted to.... Don't flame me...