Untested House, Ability score, skill and crits

[Uber Dungeon]

So my friend and I at first mocking somethings that don't make much scenes Like Dexterity (Skill and ease in using the hands) doesn't quite account for a skill such as tumble. So we thought about adding AGI to the mix and how that might work to better represent aspects of the game.
-On that topic of adding Ability scores, we figured that luck as an ability score could also represent some skills better then others also would be cool to represent critical threat range rather then by weapon. So we removed the critical threat range from weapons and are keeping the multiplier. So a Luck score of say 16-3 would give you a Short Sword, 1d6, 18-20x2. ect. (we're thinking of making a max crit rule where x3+ weapons have a max crit range of 19-20.)
Also the Luk ability score will add 1 luck reroll per point of ability modifier For use with luck feats from complete scoundrel

We're plaining on play testing this idea next weekend to see how it goes. So far we have custom made the fallowing

Feats
Lucky Fumble; Use Luck in place of STR for attack rolls.
Lucky Stumble; Use Luck in place of DEX bonus to AC

Ability Score
STR, DEX, AGI, CON, INT, WIS, CHA, LUK

Skills
Appraise _ int
Balance _ Agi
Bluff _ cha or Luk
Climb _ str
Concentration _ con
Craft _ ( _______________) ___
Decipher Script _ int
Diplomacy _ cha
Disable Device _ int
Disguise _ cha
Escape Artist _ dex
Forgery _ int or Luk
Gather Information _ cha or Luk
Handle Animal _ cha
Heal _ wis
Hide _ Agi
Intimidate _ cha
Jump _ Agi
Knowledge ( ___________) int
Listen _ wis
Move Silently _ Agi
Open Lock _ dex
Perform (______________) cha
Profession ( ___________) ___
Ride _ Agi
Search _ int
Sense Motive _ wis
Sleight of Hand _ dex
Spellcraft _ int
Spot _ wis
Survival _ wis
Swim _ str
Tumble _ Agi
Use Magic Device _ Wis
Use Rope _ dex

 

[Tovec]

I've seen something similar, though never adding a Luck ability.
When splitting Dexterity I find people will often make it into agility and speed and give bonuses to actual movement for increased speed.
The biggest problem I see in splitting DEX, even though it may make logical reason, is that the game mechanic is built with DEX in mind and many things are based on it - AC, Ref, skills, etc.
Just keep that in mind of what you are trying to quantify when changing the abilities.
Why change it, is it just to make the game seem more realistic or to balance it?

 

[Uber Dungeon]

Doing it For amusement for the most part