Shooting USPSA will hone your shooting skills, Drawing a gun from a holster, Shooting moving right & left, moving forward and backward, reloading on the move, reloading before you run out of ammo, shooting around walls and barrels. Shooting at things that are moving up, down, turning, and spinning. It will also induce stress as you have to think of what you want to do and when to do it. Many of the top instructors are now competing in matches to sharpen their skills. You need to look at USPSA, not as a replacement for your training but as an additional way to train.
I started shooting Action pistol weekly at a local club in 2009. It is geared toward self-defense. The scenarios they run are based on news reports of SD encounters, low light, no light, carjackings, robberies, knife attacks, holding your kid. As far as shooting goes I was in the middle of the pack. In May 2010 I started shooting USPAS every weekend by October 2010 I was in the top 5 shooting the local club SD scenarios. The SD scenarios were not the same as the USPSA matches but the skills you build in the USPAS matches will improve your SD skills.