One of the things I've done in a few of my games is similar to that idea. Everybody can use Combat Expertise and Power Attack for up to 5 points, with the BAB limit still in place and no doubling of the Power Attack for two-handed weapons. The Improved Combat Expertise/Power Attack feats can be taken at BAB +6, and allow you to exceed the +5 limit. Greater Combat Expertise lets you gain an additional +50% bonus to AC when wielding a long-hafted weapon (quarterstaff, spear, etc...), while Greater Power Attack lets you add +50% to damage when wielding a weapon in two hands.
It seems to work pretty well, really.