I tried this the other day.
i played 4 friendlies 1 after another and they do gain skill points nobody will get over 2 skill points after the game well not with my players anyway.
some got 2 some got 1 some gained nothing. so they don't gain as good as in a league or cup game.
tried to mix it up with high pressing one game low pressing another no difference really.

My question to myself was it worth it ?
my answer is yes and no
as at level 5 i still can make some extra $$ with attendance can add a green etc and you can try out different formations
but if i was doing it for a training skill point exercise only I'd probably say no that's my personal view anyway.
but i guess others have played it alot longer than me