Well, the wiki describes toughness as reducing physical damage. Not stopping headshots from being fatal is probably just a limit of stat; just like how even super-whatever agility you probably won't have speed much above 2000.
Hint - lower all those useless, sublime stats like Intuition, etc. And you will get a few more points. I got str, agi, tgh maxed, and the hero was pretty awesome.
Keep in mind, not all attributes are as worthless as they sound.
Creativity, Patience, Linguistic Ability, Musicality, Empathy, and Social Awareness do literally nothing in current adventure mdoe (Musicality currently doesn't do anything in Fortress mode either).
Disease Resistance and Recuperation aren't worth investing in because quick travel, sleeping, and waiting still cure all non-permanent injuries, but you probably don't want to dump them either.
Analytical Ability and Intuition are both technically used in Adventure Mode, for Knapper and Observer, but knapping is something you can train up easily and Observer is largely worthless because enemies never hide.
Memory decides how long after you see terrain do you remember what it's like.
Focus is used by Archer and Ambusher.
Willpower is used by Swimmer, and to resist passing out from pain or getting tired from overexertion.
Spatial Sense has an effect on combat, including aimed attacks.
Kinesthetic Sense affects dodging and Ambusher.