I always carry extra ammo; I just carry it in a second (or third) gun. I definitely see the wisdom behind having more ammo, but I prefer the benefits of additional guns.
I spent hours practicing reloads when I was a street cop, but all of this practice was on a range with just the clock and a target as my opponents. I think we take for granted that we will always have distance at our disposal during a lethal confrontation. I'm assuming that if a situation required more than one magazine worth of ammo, it would involve multiple attackers. If my attackers were really intent on harming me, and didn't start fleeing the second gunfire began, then I would expect at least one of them to close the distance.
I grew up wrestling and was fortunate enough to start training Brazilian Jiu-Jitsu with the Gracie family in the 90's (before it became common). In my prime I was legitimately a world class grappler. Even then, I'm not sure if I could have pulled off a reload while wrestling one or more attackers. In this rare circumstance, I would prefer to drop an empty gun and grab a full one (the classic New York reload), rather than try to get a magazine into the magwell and drop the slide against active physical resistance.
Due to my police background, people occasionally ask me if there is any particular gun that is the absolute best to have in a gunfight. My answer is: "Yes, the one in your buddy's hands". In any gunfight, having more guns on your side of the fight (in trained hands) greatly increases your odds of survival. I'm a married father, and it feels like I haven't gone anywhere alone in over a decade. If I find myself in a SHTF situation in public, I'd feel much more confident handing one loaded gun to a friend or family member than I would if I handed them any number of loaded magazines.
I do not mean to imply that my way is superior to others, it's just what I am most comfortable with. This is a decision we all have to make for ourselves, and I respect any strategy that any other responsibly-armed citizen chooses to employ.