The word that comes to my mind is "awareness". Straight pool develops your awareness of precision CB movements, precision movements of secondary OBs, speed, creativity, sequence planning, traps on the table, common layouts that work well to connect the dots so to speak.
I'm sure there are many more that could be added, but one I don't want to leave out is the awareness that there exists a pool game that is so much richer and deeper than 8 ball,9 ball, or 10 ball. A game that allows you to find that zone, that dead stroke world for much longer periods of time than any other game.
That may be the part of the game I enjoy the most. The awareness that this extended zen land exists to enjoy, and this game gives you the opportunity to find it so much more than any other.