I think all the SPs should be available from the start. For example look at order. If you have a massive empire that really benefits from it, you wont get past unlocking the 1 or 2 abilities out of 6 on the order tree. Also lategame, stuff like +1 gold or +1 production is nothing for a late-game policy. If i'm having cities with factories, banks, and universities having 50+ production, gpt, and science, that bonus is nothing.