Changing your O2s will not increase WOT power. When you hit WOT your computer goes straight to pre-programmed Air/Fuel/Spark tables. However, chaning your O2s will give you better gas milage and part-throttle response and power.
True about the O2 sensors. The spark is true for 87-93 cars only. 94-95 cars use the same spark table for part-throttle and WOT. Mike Wesely has a write up on this on the web. Very good article on why the 94-95 cars are touchy to tune compared to the 87-93 cars.