I've shot plenty of IDPA on factory ammo. That of course was when you could swing by Walmart and grab a couple of 9mm value packs for $11.98.
Round counts much higher for USPSA at any decent club. More stages, more rounds/stage, and more steel!
That said, my local IDPA club we'd often shoot the match over again with a different gun, different class or whatever. I've shot 3 matches in a night.