I have shot quite a bit of IDPA, some USPSA, some 3 gun.
I have enjoyed ALL of it, and have found the practice beneficial, for target aquisition, Shoot/don't shoot, mag changes, etc.
I have also enjoyed the many DIFFERENT scenarios, from the obvious multiple target, kill zone shooting (unlikely for a real life scenario), to the single target, shoot while retreating, from retention (VERY likely real life scenario).
I also feel VERY confident in my drawing technique (using a Serpa Blackhawk and an XD .45, and no holes in my leg as of today) and speed, both from cover (under shirt) and open (USPSA style).
The competition part of it has it's uses, both from a drawing speed aspect, but also the speed with which you aquire and shoot your target, as in you want to get off the shot before the bad guy does, obviously without shooting the WRONG target.
Range shooting has it's uses, but putting holes in the zero while standing still and taking 10 seconds to sight in only gets you so far in self defense situations, learning about cover and shooting accurately while on the move gives you a whole new perspective.
I try to shoot with a different group every month, a different RO, as I believe that each one has something to teach me, a new perspective or a different eye on my technique, all in the name of trying to be faster, more accurate, and to eye all situations from a self defense perspective, IOW, which direction do I go, which target to take out first (if there are multiples), etc.
I also know that I have fired WAY more rounds than if I were simply doing range shooting, making me a better shooter overall.