15-20 HP from CAI alone - unlikely, but it will help the off-idle response a bucket load. Generally the later model cars have (comparatively)well thought out air tracts form the factory.
Toyota developed the factory chip for the best overall response from the stock configuration. Having said that an aftermarket chip may improve the power output, but is very definitely dependant on how it is tuned.
There has been a million articles written in various publications over the years.