How important are Special Abilities?
Depend on the player position.
MLB
not very. you need all your points in attributes. every single one of them.
once you reach lvl 23 the bonus points you receive for leveling are halved. this is why its so important to put all your points into them. once you reach lvl 23 you should have 1-2 skills so high you can ride them up the rest of your career. then focus on rounding out your attributes and SA trees.

WHAT!?!?!?

My guys above level 23 still get 5 points per level.
If you're talking about the progressive cost of skills (and specials) fine, but this sounded like something else.
Maybe you meant the baseline stat increases in your primary and secondary focuses? If so, I haven't noticed but it wouldn't suprise me.
The progressive cost of skills roughly goes like 1 point if you're < 49 in a skill, 2 if your < 61, 3 and up I'm not sure cause I stop putting points in at 61 and focus elsewhere.
I'm a big fan of power leveling 1 stat for your player in this game. I have a level 14 DT w/ 61 base strength, and he is developing into a total beast.