Assuming shot placement is paramount, and that you are accurate, I'm of the persuasion that unless you get into the velocity ranges of high power rifles, there is no advantage to lowering the caliber size to gain energy. Energy dump for pretty much any modern handgun caliber is a myth IMO. If you want to see some devastating "kinetic energy dump", work up the numbers for a 90 mph fastball. Getting beaned hurts, but taking one for the team generally isn't deadly.The velocities just aren't high enough, and the same goes for any caliber that isn't fast enough to turn tissue to mush. You generally don't get those velocities out of handguns. If you get into some of the more potent revolver calibers, then maybe you might have a leg to stand on, just barely, with the whole energy thing. Otherwise I don't think it really amounts to much in terms of effectively stopping an attacker. As long as there's enough velocity to successfully penetrate an attacker's vitals, anything above and beyond that is just going to manifest itself in the forms of recoil and noise. A bigger hole, on the other hand, helps. So, IMO it's a bad bargain to give up the bigger caliber to gain more speed for these kinds of handgun calibers.
Between the .32 NAA and .380, I'll take the bigger mouse. You're already carrying the "bulk" of the bigger cased ammo, the (in most cases) larger gun, and dealing with lower capacity, why go with a smaller bullet than the gun can shoot? These necked-down calibers don't make sense to me.
Jason