Specialized technicians (CNC operators, FCs, etc.) beat the living shit out of most academics in terms of sheer income and job opportunities, bar dentists and lawyers. In these specialized technical trades, job experience is everything and no amount of college degrees will do you any good.
I think it is worth pointing out that this is still very different from going directly from high school to being a Walmart employee. You still have to study and become qualified and certified in the field before you can start to build up job experience. There are definitely opportunities to be had in this manner, but it's not quite the same thing as discontinuing education after high school.
If you're planning to go for a dime-a-dozen MBA or a major in Tibetology or something along those lines, chances are very slim that you'll find a high-paying job after college. You'll just be doing the internship runaround.
If you however specialize in subjects few to no people want and can finish, your chances will skyrocket. For example, emulsion chemistry - there's five to six capable emulsion chemists in the world, so if you're willing to bust your balls on a subject as terrifying as that, your chances will look up.
Business seems to be a high variance deal. There are opportunities to make quite a lot of money with business degrees, but at the same time, it is a crowded field and if you don't stand out, you could easily end up without a nice job.
As for superspecializing, as long as it is something that there is demand for. There are very few people with degrees in Dalcroze Eurhythmics, but there is not a lot of demand for Eurhythmicists.
If they're going to a private school just to get their undergraduate - they're wasting money. Instead of paying 20-50 grand a semester they could have spent 3k a semester at a community college and then 5-10k at a state school to finish up.
Well, yes and no. Studies have shown that in the long run, going to Harvard instead of the University of Maryland doesn't mean that you will make significantly more money on average once enough time has elapsed. Still, there is a reason people want to go to Harvard and not Bowie State. Coming out of school, all else equal, the guy with the Harvard degree is going to have an advantage starting out with regard to jobs and grad school. This doesn't mean that the Harvard guy will stay ahead if he doesn't put in good work and get results, or that the Bowie State guy can't put in better work and overtake the Harvard guy tens years in the future in terms of prestige and paycheck. Still, while the value you get in terms of (money expended/money earned) goes down by going to more expensive colleges, you are paying for something: prestige that can let you start out a little easier or a little further ahead.
I think that regardless, some form of post high school education is definitely a good idea, whether college, tech school, trade school, or another route.