I've got a Vaquero in .357, and looking at what that bullet can do from a 5.5" barrel...sure, why not?
The vast majority of civilian self-defense shootings are over in 2-3 rounds, so capacity isn't an issue. Sure, a 13-round wondernine feels reassuring, but so do my 7-8 round .45's. It's certainly enough gun.
Concealability is, of course, an issue...
Still, with new guns, I always have an "acclimation" period, where I go from being okay to being able to shoot the gun to its potential. I got to that point quicker with the SAA more quickly than I have with any other gun. It points and shoots very intuitively, and I've no doubt I could use it for self-defense.