If he has enough unassigned points to reach 6* or 7*, his training speed will be reduced. The game doesn't take into consideration that it is assigned or not. I only keep unassigned points so I can decide what to do when they reach say, 200.

So you have to probably start doing some assignments - always start with either a New Position or SA.

Again, as I have repeated many time in this forum, SA is a tricky decision. If you do not know what existing capabilities your players have, then there is no use to give them SA. SA will only boost abilities not add an ability. So if he doesn't block shots well, then he doesnt deserve a Wall. If he doesn't take freekicks well then he should not have FK abilities. You have to pay attention to the commentaries.

In terms of new positions, you need to try them in that particular position before you decide to build up tht position for them.

Special Abilities & New Positions
Having said that, what I like to do is

MC
a goalscoring MC shd be given a playmaker's ability. Playmakers in my experience are not yellow card magnets, despite what has been said before.Normally MC are better off not having more than one position. Better for MC to be more focused on one position - that's jst me, I've never had good experience with DMC/MCs or MC/AMCs.

ST
I usually try to get my ST to take corners or freekicks or pens. If they are good in either one then I assign them those respective SA.

A striker who jst doesnt score but keeps on providing assists would better be given and AMC role + shadow striker SA.

DC
A DC who likes to go forward and occassionally score should be given a DMC role + playmaker

DR/L
Most likely will get a wall as they will always block shots coming from their side.

AML/R
Try them to take corners or freekicks and give them the SA if they consistently bring in the assists from there. A freescoring winger can be given a shadow striker SA or even a playmaking SA.

After that is all done, jst assign the d@mn SPs!