Oh well, in my experience free kick specialist CM scores more often than my best striker. Strikers shooting and finishing difference is like 10 points. Still I let my striker take most of the freekicks. I believe special ability helps.
Also, I've found my corner specialist pretty useful. Corner scoring ratio increased a lot when I got him.
I use one vs one strikers, defending wall and one vs one stopper as well. I wouldn't say all special abilities are useless.