I think a better idea overall is just make all attributes more useful... One way Kirthfinder does that, is making Cha useful against mind control (which makes perfect sense IMO, in the same way that Str helps you against being grappled). Admittedly, that's much easier said than done. So reducing the number of attributes makes sense... There's value in simplicity, but the same is true for granularity, and increasing one often requires reducing the other, so we have to find a way to balance both aspects. I don't think there's that much of a benefit of having Con separate from Str, for example... And having 3 mental attributes is a bit unnecessary as well, since most mind-related checks could easily be based on "Insight" (Int+Wis) and Ego/Force of Personality/Charm/Some-word-that-sounds-way-better-but-I-can't-think-of (Wis+Cha).
Having 4 savings can be a bit much because point-buy is so limited that you'd inevitably have at least one crappy save (and I don't mean "below average, but actually "Fighter-with-low-Wis" kind of bad). Kirthfinder avoids this by making every saving throw follow the 1/2 level progression, with the character's good ones getting a +2 on top of that. This way he gets Cha to be useful without the problem of crippling characters that want to shy, taciturn and/or introvert. This is a good design IMO.
Like you said... It's indeed really dumb that a Fighter can barely afford to be decent at a single skill role while a Wizard who spends all his time in a library can be an expert climber, swimmer, acrobat, horse-rider, sailor and infiltrator because he's just that smart.
One idea that I have had in mind for freaking years now, but could never really figure out the numbers, was splitting the skill list in three separate lists... Physical/Outdoorsy skills, Intellectual/Finesse skills and Social skills. The first gets extra skill points based on Con (or maybe Str), the second on Int and the third on Cha. That by itself would make Cha super useful, while not making it a necessity for Cha who don't care much about Social skills.
I always wanted to find a good way to implement that... But it always ends up with characters have way too many or way too few skill points per level (even the dumbest, weakest, shyest character could end up with 6 skill points per level, and that's before extra from race, feats or favored class bonus). It's not necessarily a bad thing... But I didn't want the village idiot to have as many skill points as a Ranger.
I'm not sure about Divination (I played very little KF, and it was long ago), but it sounds about right. While it may look unbalanced, Charm and Compulsion effects are relatively common and usually REALLY DANGEROUS. So while the saving throw protects against only a few things, those few things are something you definitely want to be protected against.
Well, yes. That's a clear example of what I said... His attribute do tell something about the character. Just not necessarily that he just doesn't like exercising... But a person with a severe limitation to physical strength will face problems and go through situations that help form who he is. Even in modern society, where for the most part, physical strength is almost irrelevant. He's less likely to become a school bully, maybe he won't be as confident, people may treat him better or worse, he'll enjoy certain benefits that he might not remember are universal, or deal with problems that most people don't even realize exist, he could have his social life limited in certain ways (can't go play football with the guys, for example) and expanded on others (he is really good at online gaming because that doesn't require strong arms), etc...
All of that has influence on a person's mind... So a character's attributes should influence his personality so some degree. Of course, they aren't the only or even necessarily the one of biggest factors in play, but it should be there. And it kinda happens all the time even without players realizing... A Fighter with lowish Int and high Str/Dex is likely to invest his few skill points in things he wants to be good, so that probably means things like Acrobatics, Intimidate, Perception, etc and not many Knowledge checks... Which is also a possible cause and consequence of his choice of training to be Fighter instead of a Wizard... And that tells something about the character, even if the player himself doesn't realize it.