IDPA is fun and slightly more realistic trigger time than IPSC (ducking for cover - Haha - ).
I'll not argue with ya there, but it assumes that realism is a desired trait of your game of choice.
As I've heard it said:
IDPA is a game trying to be real.
USPSA/IPSC is a game that's happy to be a game.
In the end though, while I don't think either really prepares you for "situations", both tend to increase basic marksmanship skills, which you'll always do well to have in a real situation.
Also, anything is better than not shooting. I'm a USPSA person and don't do IDPA, but if USPSA wasn't around and IDPA was all that was available, I'd probably be doing that instead.