When I was MD for a local IDPA club, I was certainly aware of shooters' desire to expend as many rounds as possible. What I often did was to make each stage a series of mini-scenarios. Each one was usually 4-8 rounds, but by linking several of these together (also allows for practicing tac reloads off the clock) each stage could have as many as 18-24 rounds. This also preserved the ideals of IDPA.