Steve, re: capacity vs training -
I've been shooting since my early teens (earlier, if you count air rifles). I'm in my 40s.
Between active and reserve time, I had to qualify on the S&W M15 .38, M1911, M9, M11, M16, M4, and Remington 870. I've had fam-fires with the M2HB, M240G, M249, and Mk19.
On my own time, I shoot a lot. At least 1,000 rounds a month in practice, not counting 2x IDPA sessions per month. I've trained with Massad Ayoob for a week-long course (highly recommend Mas, and Marty Hayes, and Kathy Jackson - good people to shoot with and learn from).
I'm an NRA certified Basic Pistol instructor.
I work as a defense contractor. Have to qualify annually with sidearm and rifle. Three years running, 40/40 with pistol, and 38/40 or 40/40 with rifle.
(Edit: I also spend several hours a week at the gym and/or dojo; defensive training isn't only about firearms.)
I don't view capacity as a substitute for training. I view capacity as being much better than low capacity - assuming it is reasonably achievable.
As mentioned before, I find that a double magazine pouch makes a very nice weight and bulk offset for a concealed pistol. Adds capacity, reduces back strain (via balancing effect). I find one or two magazines (or speed strips) in weakside pocket nicely balance a pocket pistol.
There are very limited circumstances where I could carry a concealed handgun, but not be able to carry spare ammo.