Kyle,
I've primarily been talking about teenage caddies, not adults. Their priorities are different. When it comes to teenagers, I don't think your last question is really applicable. Obviously you need a group of committed kids at the core of the program. But I don't think this is something that can be demanded of all teenagers, and this is a group that basically self-selects. It depends on the facility, of course, but at some clubs I think it's good to have an "outer circle" of irregulars as well.
Some of these kids may not even be golfers themselves and will need to be taught practically everything. But someone's gotta take the Haverkamps at three in the afternoon, and I don't see anything wrong with that. These kids may get less out of the experience than the "A" caddies, but down the line they're still more likely to become golfers than the kid flipping burgers all summer.
I'm only speaking from my own (outdated) experience, but I guess what I'm saying is it takes all kinds. Looking back, I'm grateful that I was given the opportunity to essentially learn the game, its rules and its etiquette basically from nothing. I do not come from a "golfing family", so it was my first exposure to the sport, and the customs do take some learning. I'm sure guys like you and Pat Craig were infinitely better caddies than I was, but that's beside the point. My hope would be that there can still be a place in the yard for a kid to learn a few things who isn't coming to the job with a wealth of prior experience. After all, if the goal isn't to become a Tour caddie, the value of an activity like caddying is abstract, and it means different things to different people. I was half a dozen years removed from it before I realized how much I'd learned.