This is an idea I posted a while back in a differant thread, but I wanted to post a more refined version of it in it's own thread to see if this idea has legs.
As the thread I linked to is correct in saying - there is currently a gulf between Dex and Str builds. And, this may be a way to bridge that gulf a bit by making Dex have some options not open to Str builds - and make Weapon Finesse a feat worth taking. It does involve some changes to the feat as it exists, but I think they are compelling without being overpowering and would help give Dex builds some compelling options.
I would make the following two changes:
Weapon Finesse would keep the Dex-to-hit, but also give the character an additional stacks-with-everything 5% chance for a double strike.
Since Dex fighters are lighter on their feet and use more rapid and nimble strikes, I think that this change is keeping with the flavor of Weapon Finesse.
Secondly, taking the Weapon Finesse feat would open up a line of Enhancements to further the character's mastery of lightning fast and unerringly accurate strikes on their opponent.
Improved Weapon Finesse I
prerequisites: Weapon Finesse Feat, x level
AP cost: 1
Grants: An additional 2%, stacking, double-strike chance. This brings the double-strike chance to 7%
Improved Weapon Finesse II
prerequisites: Weapon Finesse I, x level
AP Cost: 1
Grants: An additional 3%, stacking, double-strike chance. This brings the double-strike chance to 10%.
Improved Weapon Finesse III
prerequisites: Weapon Finesse II, x level
AP Cost: 2
Grants: The character can now bypass one-half of their Dexterity bonus of an opponents' fortification.
My reasoning is that a character with Weapon Finesse can see the chances to strike where it hurts, and is fast enough to act upon it. It also gives a Dex character alternate avenues to be effective then Str characters possess - and give them a way to flourish. I haven't put in what levels for these only because I know that for most classes 6th, 12th, and 18th levels are already pretty tight for taking PrEs... but it would make the most sense (I think) for the enhancements to go at those levels as well.
Also, since this option of boosting a feat via enhancements exists for other feats as well (Stunning Blow, for example), this idea could work without bending existing rules too much.
Thoughts?