An intriguing idea, but I don't see a rationale behind it. It might look better like this...
Improved Combat Expertise
Unencumbered by armor, you use your weapons for defense as well as offense.
Pre-requisites: BAB +6, Combat Expertise, Dodge
Benefit: When using Combat Expertise for defense while wearing no armor, you gain a 2-point Dodge bonus to AC for every point of attack sacrificed each round, instead of the 1:1 bonus normally granted by Combat Expertise. If you do not use Combat Expertise for defense, you gain a +1 shield bonus when armed with a melee weapon.
Greater Combat Expertise
Unencumbered by armor, you use your weapons for defense as well as offense.
Pre-requisites: BAB +11, Combat Expertise, Improved Parrying, Dodge
Benefit: When using Combat Expertise for defense while wearing no armor, you gain a 3-point Dodge bonus to AC for every point of attack sacrificed each round, instead of the 1:1 bonus normally granted by Combat Expertise. If you do not use Combat Expertise for defense, you gain a +2 shield bonus when armed with a melee weapon.
Superior Combat Expertise
Unencumbered by armor, you use your weapons for defense as well as offense.
Pre-requisites: BAB +16, Combat Expertise, Improved Parrying, Greater Parrying, Dodge
Benefit: When using Combat Expertise for defense while wearing no armor, you gain a 4-point Dodge bonus to AC for every point of attack sacrificed each round, instead of the 1:1 bonus normally granted by Combat Expertise. If you do not use Combat Expertise for defense, you gain a +3 shield bonus when armed with a melee weapon.
Epic Combat Expertise (Epic Feat)
Unencumbered by armor, you use your weapons for defense as well as offense.
Pre-requisites: Epic Attack Bonus +1, Combat Expertise, Improved Parrying, Greater Parrying, Superior Parrying, Dodge
Benefit: When using Combat Expertise for defense while wearing no armor, you gain a 5-point Dodge bonus to AC for every point of attack sacrificed each round, instead of the 1:1 bonus normally granted by Combat Expertise. If you do not use Combat Expertise for defense, you gain a +4 shield bonus when armed with a melee weapon.
While I have no immediate objection to adding a Dexterity requirement, I honestly think this is a very balanced feat chain, and adding such would only bog it down. If you do insist on adding it, I would suggest that you also apply a bonus to the use of feats in the Expertise Group (Disarm, Feint, Trip) for advanced levels of this feat (+2 per feat to the contested roll?). Doing such would make this feat the 'Improved Metamagic' of fighting, and allow those feats to continue to be useful at higher levels when facing opponents that are more skilled and stronger. Note that the automatic parry bonus granted by each level does not stack with previous levels. It is a bonus that makes the feat useful even when not using Combat Expertise so you don't have an entire feat chain stinking up your character sheet when you're not prancing around like a scared fairy with an over-sized butterknife.
EDIT: Got home and checked my books for name of Combat Expertise AC bonus (Dodge), plus minor additions, changed parry bonus to shield bonus (just seems right).