Have you read Bryan Caplan's Selfish Reasons To Have More Kids? He makes a pretty strong argument that middle and upper middle class parents wildly over estimate the effects of more time and money spent on their children.

1) you never see a rational rich person sending their children to inner city public schools and making them pay for their own community college

Socialization of your children does matter, keeping them in desirable company is a good goal since on most measurable matters they have more impact than you as a parent do. Inner city schools aren't bad because there is little spending on them, indeed rural schools often get less spending on them yet outperform them. The surrounding demographics matter. The culture and incentives working on that demographic matters. We have seen schools have very little measurable impact on those except that more schooling reduces fertility.

Where we don't agree probably is that the low hanging fruit of more better people and fewer expensive criminals and morons are the fairly large minority of poor children who are brought down by lousy home environments.

We don't? I mean say there existed a pill that boosted lower class IQs to the national average, wouldn't you expect to see radical improvement? What if that pill cost thousands of dollars do we disagree providing it for free would still be an incredibly good deal? What if it wasn't a pill but a shot of retrovirus or subsidy of in vitro fertilization that takes advantage of screening for poor parents coupled with strongly promoting birth control to avoid unplanned pregnancies?

From things like the Terman study we know high IQ people create positive externalities they don't fully capture. Improvements in the genotype don't need upkeep and constant reinvestment. If you raised the average IQ of say Japan or Turkey by 15 points, you'd see nearly all of the positive effects of that persist for centuries after the program was ended. If you educate everyone to college level and then suddenly stop you see benefits persist for a generation or two at most. Investments in "nature" radically increase the gains expected from "nurture" too, since the opportunity cost of neglecting the care of a child rise dramatically in relation to the child's natural talent.

2) you see an overrepresentation of the well off children who were groomed by their parents in the professions and what you might call the rank and file of elite jobs.

You see them successfully preparing their kids for competence at those professions, I see nepotism ensuring slightly less competent people get entry jobs to excellent career tracks because of connections.

I constantly hear of studies like Preschool Education and Its Lasting Effects showing significant and persistent gains from early intervention with the right population. In the United States, that self-proclaimed paradigm of the first world.

I recall plenty of studies showing effects of most programs do wear off. The problem is many studies (I'm not commenting on the particular paper you cited) have employed no control group selected on exactly the same basis as the experimental group. This makes it virtually impossible to evaluate the effect of the treatment on gains, and the problem is made more acute by the fact that enrichment studies often pick their subjects on the basis of their being below the average IQ of the population of disadvantaged children from which they are selected. This makes statistical regression a certainty- the group's mean will increase by an appreciable amount because of the imperfect correlation between test- retest scores over, say, a one- year interval.