I shoot both IPSC and IDPA fairly regularly and shoot PPC about once a year. IPSC and IDPA are best considered skill building exercises that have some training value and can be very entertaining. Any competitive event, of necessity, will not be able to duplicate the dynamics of a real gunfight.
But,depending upon the course of fire, there CAN be training value in the process, if you are shooting the IDPA classifier or an IPSC classifier that measures basic marksmanship and gun-handling skills. Some IPSC assault courses totally lack any connection to reality and are best avoided, but classifiers and most IDPA courses of fire are at least semi-realistic.
I particularly like the USPSA Classifiers and the IDPA Classifier match as methods to test basic skills.
FoF training with AirSoft guns or the Simunitions system is MUCH more realistic from a tactical standpoint, provided that the scenarios are properly designed, realistic, and carefully controlled. It's essential that the role players understand the options they have in the scenario, and that they stay within the concept of the training. If the scenarios are unrealistic or the actors don't stay within role, the training can be worse than useless.
Training at the speed of life by Ken Murray is an excellent resource to help you design a training program using non-lethal training ammunition (NLTA)
(I went to the Simunitions Safety Supervisor & Instructor class in 2003. It was very good. I've had the oppertunity to design and run scenarios in in-service training at the PD several times since then. I still have to catch myself and make a strong effort not to design overly complex scenarios. Testing core skills in a realistic situation is more appropriate for most of us)