Agreed, but I would only allow a characterto use there BAB once.
For example, Power Attack gives a plus to damage for every point of BAB you sacrifice. Similarly, Combat Expertise allows a bonus to AC for every point of BAB you sacrifice. So, if a character had a BAB of +5, they could do:
5 points Power Attack but nothing in Combat Expertise; or
5 points in Combat Expertise but nothing in Power Attack; or
3 points in Power Attack and 2 points in Combat Expertise (or some other combination totalling to 5)
But they couldn't do 5 points of Power Attack and 5 points of Combat Expertise.
Dan